the distinct personality of an individual regarded as a persisting entity
"you can lose your identity when you join the army"
the individual characteristics by which a thing or person is recognized or known
"geneticists only recently discovered the identity of the gene that causes it"
"it was too dark to determine his identity"
"she guessed the identity of his lover"
an operator that leaves unchanged the element on which it operates
"the identity under numerical multiplication is 1"
Sameness, identicalness; the quality or fact of (several specified things) being the same.
"The two photographs are so similar that their identity is impossible to distinguish without a side-by-side comparison."
In plain English: Identity is who you are as a person, including your name, history, and the things that make you unique.
"The security guard checked my identity before letting me into the building."
Usage: Use "identity" to refer to the state of being exactly the same as something else, such as when two objects share an identical identity. Do not use it to mean a person's unique characteristics, which is the word's more common everyday sense.
The word identity comes from the Latin identitas, which entered English through Middle French. It originally referred to the quality of being identical or one and the same.