When receiving a bill from Congress, the President has several options.
If the President agrees substantially with the bill, he or she may sign it into law, and the bill is then printed in the Statutes at Large.
If the President believes the law to be bad policy, he may veto it and send it back to Congress.
Congress may override the veto with a two-thirds vote of each chamber, at which point the bill becomes law and is printed.
There are two other options that the President may exercise.
If Congress is in session and the President takes no action within 10 days, the bill becomes law.
If Congress adjourns before 10 days are up and the President takes no action, then the bill dies and Congress may not vote to override.
This is called a pocket veto, and if Congress still wants to pass the legislation, they must begin the entire process anew.