Surjective Function - All you need to know about How do you determine whether a function is onto , How many functions are onto , What is the distinction between the onto and into functions at Aakash In conclusion, onto functions are a vital concept in mathematics characterized by their ability to map every element in the codomain to at least one element in the domain. Understanding the properties, examples, and applications of onto functions is essential for solving mathematical problems and for practical applications in various fields. An onto function , also known as a surjective function , is a type of function where every element in the co-domain is mapped to at least one element in the domain. In other words, an onto function covers the entire codomain, ensuring that every possible output value is achieved by some input value.