Self-reference occurs when a statement or expression refers to itself. For example, the sentence "This sentence is about self-reference" is self-referential because it talks about itself. This concept is often explored in philosophy, linguistics, and mathematics, where it can lead to interesting paradoxes and discussions. In programming, self-reference can be seen in data structures like linked lists or trees, where a node points to itself or another node of the same type. This allows for recursive definitions and operations, making it a powerful tool in computer science for managing complex data relationships.