Readiness describes the criteria a User Story should fulfill when handed over by the Product Owner to the Team. The criteria when a User Story is considered ready should be agreed upon by the Team in a Definition of Readiness document (DOR). They usually consist of the answers to the three questions:
"Who?" (the user)
"What?" (the feature)
"Why?" (the business value)
As well as the Acceptance Criteria. The DOR should be:
Clear
Concise
Actionable