A breakout happens when price leaves a range or clears a resistance level (or support, sometimes called a breakdown). Good breakouts come with rising relative-volume and follow-through; bad ones reverse quickly into a fakeout.
Traders enter either on the break with a stop-order or on the retest of the broken level. Both approaches have tradeoffs: the first gets more fakeouts, the second misses runners.
Example: a stock has traded $48 to $50 for three weeks. It closes at $50.80 on 3x average volume. Entry $50.85, stop $49.60 back inside the range, target $54 (2x the range height).
Related: range, resistance, fakeout, retest, relative-volume