Onto is a term often used in various contexts, including mathematics and philosophy. In mathematics, it refers to a type of function known as a surjective function, where every element in the target set has at least one corresponding element in the domain. This means that the function covers the entire target set. In a broader sense, "onto" can also describe a direction or movement towards a specific goal or destination. It implies a sense of progression or transition, often used in everyday language to indicate moving from one place or state to another.