In Final Fantasy Zero, managing your speed (abbreviated SPD) is an essential component of combat. It determines the order you go in, and how much you can do on your turn, both of which can help influence whether you are on the aggressive or defensive in a given round.
Rounds and Turns
FFZ combat is turn-based, meaning that a character who is acting gets to perform their actions (generally) without interruption until their turn is over.
A "turn" in FFZ is one character's actions — when you get to tell your character what to do, it is your turn, and when another player or the GM gets to say what they're doing, it's their turn.
A "round" in FFZ is the sum of all the characters' turns (including the GM's characters).
Speed
In FFZ, how quickly you can act is when the battle starts is based on your Agility. When the battle starts, your Speed score equals your Agility. A character with the highest Speed score goes first in combat, followed by the other combatants, in descending order, until the count reaches 0. When the count reaches 0, the next round starts.
Taking Your Turn
When your turn comes up, you can generally perform a single action (such as an attack, or a spell), or you can hold your action, allowing you to take more actions in a row, later.
Holding
You do not have to take an action on your turn. If you Hold, your turn ends, but you preserve your action, and gain an additional action on your next turn. You can hold a number of actions equal to your Agility score. Characters with no Agility bonus cannot hold actions for later use — if they don't use the action on their turn, they loose the action.
Acting
The action on your turn generally consists of using one of the options from your "combat menu:" an attack, a defense, a spell, a technique, an item, or some other resource. This action may cost you MP (like most job abilities), be limited in quantity (like most items), or give you a wait time (most attack and defense options).
If you have more than one action on your turn, from holding, you may do multiple actions at once, with one caveat: any ability with a wait time can only be performed once per turn (though you can perform multiple different abilities with wait times). Wait times are added up and applied after all actions are finished.
Wait Times
Delay and Charge are "wait times." Not every action has a Delay or a Charge, but those that do subtract from your Speed score.
A Delay decreases your Speed score after you execute the ability. This affects when you can go on your next turn. Delays generally run from 0 to 5, and generally offset simple powers.
A Charge decreases your Speed score before you execute the ability. This affects when you take this turn: on your turn, choose your ability, and then you go next when your new, lower Speed would dictate. Charges generally run from 0 to 5, and generally enhance more complex powers.
Your Next Turn
At the end of the round, the next round begins, counting down from the highest Speed score.
Losing Turns (Speed < 1)
A character with a low Speed, or one who uses many Wait Times, may wind up with a "negative Speed." If this happens, they gain +5 Speed, but cannot go on this round.
If a delay causes you to miss a turn, you still execute your attack, you just wait.
Defend
The Defend action means that you are protecting yourself from harm, taking a passive role during the round. You gain a bonus on your Speed equal to your Agility score (in addition to other effects).
