The story
From the movement of a crab, which appears to move sideways and seems to be going neither forward (a bull market, in this metaphor) or backward (a bear market).
Etymology from Wiktionary, CC BY-SA 4.0.
crab market
Today it means: A market trend where a stock keeps fluctuating around the same price over a longer period of time, neither entering a bull market nor a bear market Full definition →