These numbers are located on the aircraft tail, so they are sometimes referred to unofficially as "tail numbers". On the Northrop Grumman B-2 Spirit bomber, lacking a tail, the number appears on the nose gear door.

Yes. Google the tail number including the prefix (N) for US registrations and there will be an FAA supplied page that will give you the owner and other pertinent information. If you don't know just by looking at it and remembering who owns what plane, you can look it up in the FAA aircraft registration database.

In the United States, the registration number is commonly referred to as an "N" number, because all aircraft registered there have a number starting with the letter N. An alphanumeric system is used because of the large numbers of aircraft registered in the United States.

A tail number refers to an identification registration code (letters, numbers, or both) painted on an aircraft, frequently on the tail. Tail numbers can represent: An aircraft registration number (civil aviation) United States military aircraft serials.