Definition
A movement that uses more than one joint and muscle group at once, such as a squat, press or row, as opposed to an isolation exercise like a curl.
Compound: squat, deadlift, bench press, row, overhead press, pull-up, lunge. Isolation: curl, extension, raise, fly.
Compounds come first in a session because they train the most muscle per set, carry the most load, and transfer to life and sport. Isolation work fills the gaps afterwards. Roughly two thirds compound and one third isolation covers most programmes.
For beginners, compounds are also skills. Keep the reps moderate, 5 to 8, while the technique is being learned.