Float
The number of shares available for public trading - excludes insider and institutional locked-up shares.
Low-float stocks are volatile: a moderate buy/sell imbalance can move them 20% on the day. High-float large caps absorb order flow without much price movement. Float matters most to day traders looking for explosive movers.
Learn to actually use Float.
Definitions are the easy part. The free first five modules put this on a real chart and make you do the work. No card required.