A prompt is the input text given to a model to elicit a response — can range from a single question to a multi-section document with instructions, examples, and constraints. Prompt engineering has emerged as a discipline for crafting inputs that reliably produce desired outputs. System prompts set behavioral guidelines, while user prompts carry the actual request. The effectiveness of a prompt depends on the model's training, the task complexity, and how well the prompt leverages the model's capabilities through techniques like chain-of-thought or structured formatting.