What does it mean for a function to have one to one mapping?

One to one mapping means is that there's only one value you could insert into the function that would give you a certain output. f(x) = 2x+1 is an example of one to one mapping where 3, for example, is the only value you could use as an x-value which would give you 7. In this way each possible input value is matched "one to one" with each possible output value. One to one mapping is useful as it means you can find the inverse of the function.

A function which doesn't have one to one mapping is g(x) = x² since inputting either 2 or -2 as the x-value would both give an answer of 4. This means g(x) has many to one mapping.