ELIZA is an early computer program created in the 1960s by Joseph Weizenbaum. It simulates conversation by using natural language processing techniques. The program is designed to mimic a psychotherapist, responding to user inputs with questions and reflections that encourage further dialogue. ELIZA operates by recognizing keywords and phrases in the user's text, then generating responses based on pre-defined patterns. This simple yet effective approach allows users to feel as if they are engaging in a meaningful conversation, despite the program's limited understanding of context and emotion.