A shakeout is named after the fact, when the recovery has already happened. At the time it is indistinguishable from the start of a reversal, which is exactly why it works: the holders who sell do so because the move is genuinely ambiguous.
The term is often used to avoid accepting a loss - calling every decline a shakeout is copium with a technical vocabulary. It has meaning only if you defined beforehand what would separate a shakeout from a break, usually a level and a closing basis. See weak-hands.
Related: weak-hands, liquidity-grab, fakeout, copium