Quick answer: a full out is a complete run-through of a team's routine, performed at full competition effort from start to finish without stopping - used in practice to build stamina, consistency and performance quality ahead of an actual competition.
What the Term Means
Unlike drilling individual sections of a routine, a full out means performing the entire routine - every stunt, tumbling pass, jump and formation change - continuously and at full intensity, exactly as it would be performed on a competition floor.
How It's Used in Practice
Coaches typically use full outs to test whether a team can maintain difficulty and execution across the full length of a routine, since fatigue in the later sections of a routine is a common source of deductions that don't show up when practising shorter sections.
Why It Matters
A team that can consistently hit zero on full outs in practice is generally considered ready to compete, since a full out is the closest practice equivalent to an actual competition performance.
How the Term Is Used
"Full out" is used both as a noun ("we did three full outs today") and to describe the standard of effort itself ("perform it full out"), meaning at full intensity rather than marking through the motions.
Related Terms
See What Is a Cheer Routine? for what's being performed, and Warm-Up for how a team prepares before a full out or a competition performance.