In NCERT Class 12 Maths, one-one (injective) and onto (surjective) functions are two important types of functions:

- One-One Function (Injective): A function is one-one if different inputs give different outputs. This means no two elements in the domain map to the same element in the codomain. Example: f(x)=2x is one-one.

- Onto Function (Surjective): A function is onto if every element in the codomain has at least one pre-image in the domain. This means the function covers the entire codomain. Example: f(x)=x3 is onto for real numbers.

A function can be both one-one and onto (bijective).