The sharp move is the pole; the tight pullback is the flag. A bull flag drifts down or sideways after a rally on falling volume; the breakout above the flag on rising volume is the entry. Bear flags mirror this.
The measured target is the pole height added to the breakout point. Flags fail when the pullback retraces too much of the pole or when volume does not confirm.
Example: a stock runs from $20 to $26 in two days (pole), then drifts to $24.50 over three days (flag). A break of $25.20 targets $25.20 + $6 = $31.20.
Related: breakout, pullback, volume, head-and-shoulders