1 : the act of finding out who someone is or what something is : the act of identifying someone or something [noncount] ▪ A member of the family was brought in for identification of the body. ▪ The birds are tagged for easy identification. [count] ▪ The police have made a positive identification of the suspect.
2 [noncount] : something that shows who a person is : a document, card, etc., that has your name and other information about you and that often includes your photograph ▪ We were told to carry (some) personal identification at all times. ▪ He needed to show (his) identification before they would cash the check. ▪ You need two forms of identification.
3 [noncount] : a feeling that you share and understand the problems or experiences of another person : the act of identifying with someone ▪ the movie audience's identification with the good guys ▪ They had/felt a (strong) sense of identification with their neighbors.