A rule where the maximum bet or raise is the current size of the pot.
The cap is "the pot after you call." Mental shortcut: "last bet × 3 + the pot before it." At 1/2, the maximum first raise is 3 × 2 + 1 = 7 (3.5bb). PLO and PLO8 use this rule, and with deep stacks you cannot get everything in with a single bet.