Acceptance criteria are story specific requirements that must be met for the story to be completed. They are a technique for adding functional detail to user stories. Acceptance criteria are often added during backlog refinement or during the sprint planning meeting.
Some examples of acceptance criteria:
No password longer than 16 characters should be allowed
VAT should be included in all figures
These acceptance criteria add details to the user story and they also provide a convenient guide for testing the completeness of the story.
Definition of done
The definition of done is a list of things that need to be completed for any story to be considered done.
The definition of done is agreed by the team prior to starting work. It covers what the team feels is necessary to consider any story done.
Examples might be:
Regression testing completed
User documentation updated to reflect new story
Seen by and approved by the Product Owner
Performance testing benchmark achieved