How can a bill pass if the President vetos it?

There are four things that can happen to a bill.

The first thing is the president can sign it and it goes into law.

The second thing is the president allows the bill to go into law without his signature. If the bill sits on the president's desk for ten days and Congress is still in session, the bill automatically becomes law. This happens to two kinds of bills: boring bills that just make real small technical changes to laws, and bills that the president doesn't really like but doesn't have any reason to veto either.

Third is the pocket veto. If Congress is out of session when the 10 days elapses, the bill dies. It's like he put it in his pocket and forgot about it, which is how it gets its name.

And fourth is the veto. The president marks "veto" on the bill, states his objections to it and sends it back. At this point Congress has three options. The first is to make the changes the president wants, revote the bill and send it back to the White House for signature. This generally does NOT happen. The second is to revote the bill as it stands, and it becomes law should two-thirds of both houses vote for it. The third is just to let the bill die.

Sometimes you'll hear that a bill has a veto-proof majority in one or both houses of Congress. This means at least two-thirds of the members of that house voted in favor of the bill. It also means the president doesn't like it.