You might need just the “last four” of it: Abbr.

The answer to this crossword question is SSN. SSN is an abbreviation that stands for Social Security Number. When someone uses the phrase “last four” with regards to an SSN, they are referring to the last four digits of a person’s Social Security Number. This phrase often comes up in situations where someone needs to verify their identity, such as when applying for credit or filling out important paperwork.