Final answer:
A bill is proposed legislation still under discussion, while a law is an enacted bill. With less than 10 days before Congressional adjournment, a bill not signed by the President will not become law due to a 'pocket veto', and cannot be overridden since Congress is not in session.
Step-by-step explanation:
A bill is proposed legislation under consideration by a legislature. A law is a bill that has been passed by both the House of Representatives and the Senate and has been approved by the President or allowed to become law without the President's signature, as outlined in Section 7 Clause 2.
When Congress sends a bill to the President, and there are less than 10 days before Congress adjourns, the President can opt not to sign the bill and let it die. This is known as a pocket veto. Normally, if the President does not act on a bill within ten days (not including Sundays), it would automatically become a law.
However, if Congress adjourns during that ten-day period and the President has not signed the bill, it does not become law. A pocket veto cannot be overridden by Congress since the legislature is no longer in session.
This situation is starkly different from a regular veto, where the President returns the bill with objections to Congress, allowing them an opportunity to override the veto with a two-thirds majority in both houses.