Targeting is complicated, but targets are both the initial targets (creature, object or point of origin that you direct a spell at), and creatures & objects affected by the spell's effect(s)
D&D 5e is written using natural language, and terms use their natural meaning unless otherwise specified by the game. As a result, for the purposes of spells, we need to check the section on targets to see if it defines what a target is.
Note/Disclaimer: Throughout this answer I will be leaving out sections of quoted text to try and get to the essence of what counts as a target. I have done my best not to leave out any relevant information, while cutting out as much irrelevant information.
The rules that set out targeting, are in the PHB section on Casting a Spell:
Targets
A typical spell requires you to pick one or more targets to be affected by the spell's magic. A spell's description tells you whether the spell targets creatures, objects, or a point of origin for an area of effect.
[...]
There are three important pieces of information to extract here:
- A typical spell requires you to pick one or more targets (Read: Not all spells will require you to pick a target), however all spells have targets (as specified by the second sentence)
- The spells description will tell you what it can target
- Spells target creatures, objects or points of origin for areas of effect. We have a new game term that we need to investigate to find more information on targeting, "area of effect".
- The term target is not defined as a game term, thus we must use its natural language meaning (meaning all dictionary definitions are in scope)
Let's address that last point before moving on:
Target is not defined as a game term, therefore it takes on its natural language meaning (ie its meaning in English per the dictionary).
Cambridge defines target as:
to aim an attack, or a bullet, bomb, etc., at a particular object, place, or person
...
A target is also a person or group attacked in some way
Merriam-Webster defines target as:
1a. a mark to shoot at
...
1c. something or someone fired at or marked for attack
...
2b. something or someone to be affected by an action or development
To boil all that down, a target is either:
- Something at which some sort of attack or effect is aimed at. So in essence, your target is the creature, object or point of origin that you are aiming the spell at
- A target is also "something or someone to be affected by an action or development". So a creature caught in an AoE can also be described as a target by virtue of being affected by the spell.
Now that we have the dictionary back on the shelf, let's move on to examining other elements of the game for targeting information. As D&D is an exceptions based game...we may have something that contradicts the above dictionary definition, so we should more thoroughly examine the Casting a Spell section for targeting information.
Almost straight away we find a relevant section, Range:
Range
The target of a spell must be within a spell's range. For a spell like magic missile, the target is a creature. For a spell like fireball, the target is the point in space where the ball of fire erupts.
Most spells have ranges expressed in feet. Some spells can only target a creature (including you) that you touch. Other spells, such as the shield spell, affect only you. These spells have a range of self.
Spells that create cones or lines of effects that originate from you also have a range of self, indicating that the origin point of the spell's effect must be you (see "Areas of Effect" later in this chapter)
Once a spell is cast, its effects aren't limited by its range, unless the spell's description says otherwise.
So this section has given us a wealth of information on targeting that we should account for:
- It has given us specific examples of spells that target creatures and points of origin for us to compare (which should help clarify things)
- If a spell has a range of touch it targets a creature (or possibly an object...exceptions are a thing!)
- If a spell has a range of self it either targets you (a creature) or it targets a point of origin for an area of effect, but that point of origin is you, the creature.
- Just because a spell has an initial target, that does not mean it cannot affect other things once it has been cast (ala cloudkill).
- We need to look at the Area of Effect section for more information on points of origin
Now that we have two sections of Casting a Spell "shouting" at us to look at the Areas of Effect section for exceptions clarifications. We should do that:
Areas of Effect
[...]
A spell's description specifies its area of effect, which typically has one of five different shapes: cone, cube, cylinder, line or sphere. Every area of effect has a point of origin, a location from which the spell's energy erupts. The rules for each shape specify how you position it's point of origin. Typically, a point of origin is a point in space, but some spells have an area whose origin is a creature or an object.
A spell's effect expands in straight lines from the point of origin. If no unblocked straight line extends from the point of origin to a location within the area of effect, that location isn't included in the spell's area. To block one of these imaginary lines, an obstruction must provide total cover, as explained in chapter 9.
[...]
A cone's point of origin is not included in the cone's area of effect, unless you decide otherwise.
[...]
A cube's point of origin is not included in the cube's area of effect, unless you decide otherwise.
[...]
A cylinder's point of origin is included in the cylinder's area of effect.
[...]
A line's point of origin is not included in the line's area of effect, unless you decide otherwise.
[...]
A sphere's point of origin is included in the sphere's area of effect.
We have some more really good targeting relevant information here:
- A point of origin can simultaneously be a creature (huzzah!)
- Depending on the shape the spell produces as an AoE the point of origin either is included, or may be included at the discretion of the spell caster
- An area of effect can be any shape, but is typically one of 5 shapes.
- All areas of effects have a point of origin
Conclusion
Now to bring that all together we can say:
A target is the creature, object or point of origin that you direct a spell at as well as creatures & objects affected by the spell's effect(s).
In general, the spell's description specifies what the target is.
In some cases it is not necessary for the spell's description to specify the target, because the range specifies it for you (Shield being a perfect example, Range is Self, therefore it targets the caster). If the range of a spell is touch
If a target is a point of origin it is:
- possible for it to simultaneously be a creature/object and a point of origin
- possible, depending on the AoE shape that will be created, for the point of origin not to be included in the AoE at the whim of the spell caster
- possible for more than the point of origin to be affected by it, and thus become a target of the spell
Let's take all of this and construct a "concrete" example using the Spiritual Weapon spell. The description of the spell states:
You create a floating, spectral weapon, within range [...]
[...] you can make a melee weapon attack against a creature within 5 feet of the weapon.
[...]
The weapon can take whatever form you choose.
This excerpt has a plethora of targeting information in it:
- A floating spectral weapon is created by the spell. Since the spell isn't initially targeting a creature or object, it must be targeting a point of origin to create an area of effect. Well what is that area of effect I hear you ask? The area in which there previously was no spiritual weapon, where there is now a floating, spiritual weapon. So it targets a point in space.
- Once the spiritual weapon is created, the spell allows you to move it, and make attacks against creatures with it. Therefore the spell is now targeting the object that is the spiritual weapon. So it also targets an object.
- The spiritual weapon can attack creatures within 5 feet of it. Those creatures are most certainly being affected by the spiritual weapon smashing their face in. Thus it is now also targeting one (or more) creature(s).
- Importantly it can only attack creatures...which means all other objects are safe from the floating menace that it the spiritual weapon.
From this somewhat innocuous spell we can see a few things:
- targeting is not limited to only one of the three options we are given (creature, object or point of origin)
- the target of a spell can change throughout the spell
- it is possible for spells to target all three categories of targets from a single invocation
Note: One could also make the argument that the caster is also the target of the spell as it changes them to give the caster control over the weapon. I don't find this line of reasoning compelling (personally), as the caster, in the case of this spell, is the source of the magic and is targeting a set of things external to themselves. However I can see how a person could find that line of reasoning compelling.
Caveat to the above
D&D is an exceptions based game, and therefore it is conceivable that some spell will change or add to the targeting.