Bucketing lets you quickly categorize report records without creating a formula or a custom field. When you create a bucket field, you define multiple categories (buckets) used to group report values.
For example, get a view of your accounts based on how many employees they have. Create a bucket column named Size based on the # Employees field. Then, create buckets that group records into Small, Medium, and Large ranges that you define. Small includes accounts with 5,000 or less employees. Medium includes accounts with 5,000 to 10,000 employees. Large includes accounts with more than 10,000 employees. Now you can sort, filter, or group records based on how they’re grouped in buckets. If one account grows or shrinks, it’ll automatically switch buckets.
Bucketing lets you quickly categorize report records without creating a formula or a custom field. When you create a bucket field, you define multiple categories (buckets) used to group report values.
For example, get a view of your accounts based on how many employees they have. Create a bucket column named Size based on the # Employees field. Then, create buckets that group records into Small, Medium, and Large ranges that you define. Small includes accounts with 5,000 or less employees. Medium includes accounts with 5,000 to 10,000 employees. Large includes accounts with more than 10,000 employees. Now you can sort, filter, or group records based on how they’re grouped in buckets. If one account grows or shrinks, it’ll automatically switch buckets.
https://help.salesforce.com/articleView?id=reports_bucketing_overview.htm&type=5