Candlestick
A single-period price bar showing open, high, low, close (OHLC).
Body = range between open and close. Wicks = the highs and lows price tested before closing. Green (or hollow) = close above open. Red (or filled) = close below open. Reading candles individually is noisy; reading them in sequence is where the information lives.
Learn to actually use Candlestick.
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.