[Bruno]

Originally Posted by jtsmith1287

So, the Basic Sets seems to use the word "turn" rather loosely. I've noticed that a turn can be the one second where a PC acts, and a turn is also the entire round of combat, since the entire round is in fact just one second that everyone acted in.

No, it uses it very consistently. It's just that it's neither of the things you think it is, and that's causing some cognitive dissonance. This is pretty common and I think a little diagram in the BS would have cleared it up, but what do you cut to make room for the diagram? :D

Andy, Bob, and Chuck get in a fight, and their Basic Speeds happen to arrange them in alphabetical order.

Their turns overlap. It takes one second between Andy's chances to act, and between Bob's chances to act, and between Chuck's chances to act. But when Bob acts, it's not the start of second #2, and when Chuck acts it's not the start of second #3. WHen andy gets his second turn, it's the start of second #2 of the fight, not #4.

When they act, it's resolved as if their action takes place "instantly" as a simplification for game purposes, but technically everything they do from when they choose their maneuver to when they choose their maneuver again is "one second" and can be looked at as one complex event; we just look at little slices of it to figure out what happened.

|-1- Andy -----------|-2- Andy -----------|-3- Andy ------
        |-1- Bob ------------|-2- Bob ------------|-3- Bob
                |-1- Chuck ----------|-2- Chuck ----------|

Originally Posted by jtsmith1287

So my question is clarification on defending. You may only block once per turn. So, I'm assuming this means that if two people are attacking the same PC then that PC only can block one of those attacks. They could also parry, but at a penalty for each attack, correct? And dodging, if I'm not mistaken, can be done against any number of attacks and any point during the "round".

All correct.

As a note, "Round" is not a term from GURPS, so I'm thinking part of your confusion is that rules from some other game are getting tangled in with the GURPS rules?

Originally Posted by jtsmith1287

Also, you can only do an acrobatic or retreating dodge once per "round"

No, per turn. Remember, no rounds.

Originally Posted by jtsmith1287

, so does that mean that once a player has done that they also forfeit their other active defenses, since it takes up that entire maneuver?

It's not a manuever. It just means exactly what it says: You can only do ONE acrobatic or retreating dodge per turn. It doesn't restrict anything else.