Bijection

A bijection is a perfect pairing between two sets, meaning every element in one set is paired with exactly one element in the other set, and vice versa. In other words, every item maps uniquely to a partner, with no leftovers or overlaps. This creates a one-to-one correspondence that connects every element in both sets without repetition or omission. Bijections are important because they show when two sets have the same size or structure, even if the elements themselves look different. Think of it like matching socks to their drawers—each sock has exactly one matching drawer, and each drawer holds exactly one sock.