Level 2 Data
Also called: level II, market depth, depth of book
Level 2 data shows the order book beyond the best bid and offer, with sizes at each price level. Retail platforms sell it as an edge, and it is genuinely useful for sizing an exit in an illiquid name. For short-term prediction it's largely obsolete: professionals see it microseconds earlier, and much real liquidity is hidden in iceberg orders and dark pools that never appear in it.