A parameter that controls how random or deterministic a model's output is. Temperature 0 makes the model always pick the most probable next token (deterministic, focused). Temperature 1+ makes it more willing to pick less probable tokens (creative, unpredictable). Most APIs default to around 0.7.
Why it matters
Temperature is the creativity dial. Writing fiction? Turn it up. Generating code or factual answers? Turn it down. It's one of the most impactful parameters you can adjust, and it costs nothing to experiment with.