Monsters description and number of attacks

Question

I need some clarification about how many attacks a monster can do and the way this is specified in the monster description.

I noticed that these entries are separated by "," or "and". Is there any difference or do both have the same meaning?

Then if a monster has multiple attacks (natural or not), how many of them can it do in a stabdard action?

For example, a dragon has bite, 2 claws, 2 wings, tail slap. In a full attack it gets 6 attacks, no questions, but what about in a standard action (let's say after a move)? Does it still have 6 attacks or must it choose only one of them?

And what about a Marilith? With:

+1 longsword +24/+19/+14/+9 (2d6+8/17–20), 5 +1 longswords +24 (2d6+4/17–20), tail slap +17 (2d6+3 plus grab) or 6 slams +22 (1d8+7), tail slap +17 (2d6+3 plus grab)

... I'm more confused. Does this mean that it has ( 4 attacks (+24/+19/+14/+9) and/or 5 attacks (+24) and/or tail slap ) or ( 6 slams and/or tail slap )?

Generally I don't always understand where/when the "," is an and or an exclusive or.

Answer 1

This issue becomes clear once the rules on actions in combat and natural weapons have been carefully studied.

A good way to understand what kind of action each type of attack requires is to think of the actions first. Go to the standard action subheading and observe that it only allows you to make a singular "attack". The "full attack" option, which describes how to attack multiple times in a round, is described under full-round actions. (In short: Standard action = one attack, full-round action = all attacks)

As for the Marilith, the comma separating items in its full attack list is an AND. Thus, the full attack line describes two options:

1. Making its normal number of iterative attacks (stemming from its BAB of +16) with its primary weapon, followed by 5 attacks from its secondary weapons (held in other arms), followed by a single tail slap.
2. Foregoing all of its sword attacks to perform natural slam attacks with all of its appendages, and then a single tail slap.

Answer 2

The same rules from the core rulebook apply to monsters as well as characters. Any creature has only one attack as a standard action. Those lines are for full attacks, where they get everything separated by commas ("ands"), but have to choose between the "or"s.

So on a full attack the marilith can choose between 9 swords (including the iterative attacks on the primary sword) and a tail slap or 6 slams and a tail slap.