Only 4 spells in D&D 5e meaningfully use the word spot (thanks to techurbana for the list) as a place where something happens:
Silent Image - The image appears at a spot within range
Major Image - The image appears at a spot that you can see within range
Tree Stride - You appear in a spot of your choice within 5 feet of the destination tree
Dimension Door - You Teleport yourself from your current location to any other spot within range.
What does "spot" mean here?
Is it like a point of origin, as many other spells have, meaning you need direct line of sight with it? This implies that mentioning the that you can see clause in Major Image is redundant.
Is it just any point we desire? This implies that we can choose a point under the ground, for example, but it would mean that Silent Image (a level 1 spell) has lighter requirements than Major Image (a level 3 spell), in the sense that Major Image cannot be cast behind walls and stuff like that.
Is it the same as an unoccupied space? Many spells refer to unoccupied spaces as targeting locations. Does this mean that you cannot cast these illusions around, say, a treasure chest, to protect them, since the space is occupied?