What's the English word for math identity units like identity matrix or number 1?

There was one word professor mentioned in class I could not remember, it means anything that will always retain the value of the other in multiplicat

There was one word professor mentioned in class I could not remember, it means anything that will always retain the value of the other in multiplication, like number 1, x*1=x, or identity matrix, A*I=A.

or:There was one word professor mentioned in class I could not remember, it means anything that will always retain the value of the other in multiplication, like number 1, x*1=x, or identity matrix, A*I=A.

or:The word is identical. Identical or identity means two things are the same by definition. Equal means they happen to be the same in the stated case.

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