Full explanation — Outs
Outs are the unseen cards that can improve your hand into the best hand at showdown. Counting outs is a fundamental skill: a flush draw has 4 outs, an open-ended straight draw has 8, and so on. The 2x/4x rule lets you quickly estimate equity from outs — multiply outs by 4 for two cards to come (turn and river), or by 2 for one card to come (river only).