Full Idea
An 'injective' function is 'one-to-one' - each element of the output set results from a different element of the original set.
Gist of Idea
An 'injective' ('one-to-one') function creates a distinct output element from each original
Source
Peter Smith (Intro to Gödel's Theorems [2007], 02.1)
Book Reference
Smith,Peter: 'An Introduction to Gödel's Theorems' [CUP 2007], p.8
A Reaction
That is, two different original elements cannot lead to the same output element.