What is the difference between a rough estimate and a detailed estimate?

Rough estimates are loose estimates that you can add to backlog items for use in prioritizing the backlog and for release planning. You don't have to use rough estimates if you don't need them. Rough estimates are specified in the "Rough estimate" field in backlog items:

Detailed estimates are the estimates used for planning sprints, and in the ongoing work during the sprint, such as in the task board and the burndown charts. They are also used in Kanban boards. Detailed estimates are used in the "Estimate", "Used", and "Remaining" fields in backlog items and tasks:

Rough estimates are completely separate from detailed estimates, and you can use different units for them, such as points for rough estimates, and days or hours for detailed estimates.