Breakout

A breakout is a push through a price level that has repeatedly capped a stock, usually a prior high or well-tested resistance, on volume heavier than the sessions that built the level. The level matters because sellers defended it before; the volume matters because it shows those sellers are finally absorbed.

Once price clears the level, two mechanical forces feed the move: buy stops from short sellers positioned against the level, and momentum traders whose scanners flag the new high. A break on 4-5x normal volume has fuel. A break on light volume is a coin flip and frequently becomes a fakeout.