Temperature is a parameter that controls the randomness of a language model's output. At temperature 0, the model always picks the most likely next token (deterministic, repetitive). As temperature increases, the model assigns more probability to less likely tokens, producing more diverse, creative, but also more unpredictable output. A temperature of 0.7 is common for conversational AI; 0.2 for factual question answering; 1.0+ for creative writing. It is one of the most important settings in prompt engineering.