identification number—a number or string of numbers used to identify someone; "she refused to give them her Social Security number." 2. ID card — a document that contains a person's photograph, name, address, and other information about that person. The term is usually applied to a driver's license or state-issued identification card. 3. Identification mark — any distinctive mark, such as a logo or color scheme, used by one company to identify themselves to others. 4. Identification tag — a small piece of paper with some identifying information about its subject attached. These can be used to track items such as books in a library or pets at a pet store. 5. Identification number - A number or string of numbers used to identify someone. This number may be found in a person's passport, driver's license, social security card, credit card, phone bill, or other documents. It can be used to identify that person or their record in a database. 6. ID badge - A badge showing an identification number for use by employees or students who must show proof of identity to enter a school building or perform other duties.