Spike

A time-boxed investigation or research task used to reduce uncertainty before estimating or implementing a user story. Spikes are added to the sprint backlog when the team lacks sufficient knowledge to estimate a story confidently. A spike produces knowledge as its deliverable — a proof of concept, a research summary, an architectural decision, or a working prototype — rather than shippable product functionality. Spikes are always time-boxed: the team commits to spending a fixed amount of time (e.g., two days) on the investigation regardless of the outcome. The insights from a spike inform the story's estimate and implementation approach in a future sprint.