A more thorough explanation:

A pocket veto is a type of veto used by the President of the United States. If the President receives a bill from Congress and does not sign it within ten days, the bill does not become a law. This is called a pocket veto because the President does not have to formally veto the bill, but can simply "pocket" it and let it expire.

For example, if Congress passes a bill and sends it to the President on December 20th, and the President does not sign it by December 30th, the bill will not become a law. This is because Congress is not in session during the last ten days of December, so the President cannot send the bill back to Congress with a veto.

The use of a pocket veto can be controversial because it allows the President to effectively veto a bill without having to take a public stance on it. However, it is a power granted to the President by the Constitution.