Most of the good info has already been provided. So I will provide more.
Creep applies mainly to single action trigger pulls. Double-action trigger pulls don't have creep. To understand why, let's look at how a single-action trigger is supposed to work.
Takeup is the initial "slack" built into the trigger system. Some single action trigger pulls, such as those on some revolvers, have no takeup at all (or close to it). The amount of resistance in the takeup is close to zero.
Once the trigger is pulled through the takeup (if any), the single action trigger
should not move at all until a certain pressure threshold is crossed. Once that exact threshold (the pull weight of the trigger) is crossed, the trigger "breaks" in one very short movement, and the hammer falls.
Creep is when you have pulled the trigger through the initial takeup, but you can feel the trigger moving back before it breaks, usually in a gritty and irregular fashon. Because it is uneven and inconsistent, creep makes it more difficult to shoot with precision consistently.
Creep doesn't really apply to a double-action trigger, since the trigger is
supposed to move through the entire pull. When the double-action pull is uneven it is usually called "stacking."
the top national shooter (or one of them anyhow) prefers some creep or a trigger that "rolls"
IIRC Rob Leatham likes them that way. However, the "rolling" letoff isn't really creep, because it is consistent, smooth & designed into the trigger. Single-action triggers can be creep-free but vary in the degree of the subjective "sharpness" of their break.