A pocket veto is a slightly sneaky way for a president or governor to veto a bill. If Congress gives the president a bill and the president doesn’t sign or reject it, the bill isn’t passed. That’s a pocket veto.
In the US, either a state governor or the president can attempt to use a pocket veto. The president, for example, is required to respond to bills within ten days (either passing or vetoing them), or else they automatically become laws — unless Congress isn't in session, in which case the bill dies, or undergoes a pocket veto. It’s like the president stuck the bill in her pocket and forgot about it. It turns into a “no.”