All glossary terms
Plan
Acceptance criteria
Acceptance criteria are the conditions a story must satisfy to be considered complete, testable, bounded statements describing what the system does. Good AC are behavioural (user-visible outcome), not implementation-specific (database schemas).
AC and the Definition of Done are siblings: AC are story-specific, DoD is team-wide. AC come in two common formats: bullet list ('System returns 200 when payload is valid; system returns 400 with field-level errors when payload is invalid') and Gherkin scenarios. Both work; pick one per team and stick to it. The point isn't the format, it's eliminating ambiguity at planning time so 'done' has the same meaning to PM and engineering.