Backlog refinement, also known as backlog grooming, is an ongoing process in Scrum where the product owner and the development team collaborate to ensure that the items on the product backlog are relevant, detailed, and estimated to a degree appropriate to their priority. The goal of backlog refinement is to get product backlog items in a "ready state" so that the development team can complete them in a sprint, thereby creating a usable increment of value.

Some of the activities that occur during backlog refinement include adding details to items, such as description, order, and size, removing user stories that are no longer relevant, creating new user stories in response to newly discovered needs, and re-assessing the relative priority of stories. The product owner should refine the product backlog before each sprint planning meeting.

Backlog refinement is an important tool in the product development process because it helps the development team build only the features and functionalities that the customer wants and the business needs. It is an ongoing activity that paves the way for future sprints and ensures that the backlog remains populated with items that are relevant, detailed, and estimated to a degree appropriate to their priority.

In summary, backlog refinement is an ongoing process in Scrum where the product owner and the development team collaborate to ensure that the product backlog items are in a "ready state" so that the development team can complete them in a sprint, thereby creating a usable increment of value.