A bucket column is a feature within the Salesforce report builder that allows users to categorize report values on the fly without altering the source data. Users can define "buckets" and group multiple values from a source column, such as a picklist, into a single category. This directly addresses the sales rep's need to categorize multiple picklist values into a single value for reporting purposes, for example, grouping various industry picklist values into broader sectors.

B. Unique Count: This is a summary function used to count the number of distinct values in a report column, not to categorize them.

C. Report Filter: Filters are used to include or exclude records from a report based on specific criteria, not to group or re-categorize values.

D. Chart: A chart is a visual representation of report data. While it can display categorized data, it does not perform the categorization itself.

1. Salesforce Help Documentation: "Bucket Columns in Salesforce Reports." This document states, "Bucketing lets you quickly categorize report records without creating a formula or a custom field... For example, create a bucket column to categorize accounts by size based on the Number of Employees field." This directly supports the use of bucketing for categorization.

2. Salesforce Trailhead: "Reports & Dashboards for Lightning Experience" module, "Categorize Data with Bucket Columns" unit. This official training material explains, "Bucketing is a tool in the report builder that lets you quickly categorize report records... For example, say you want a report that groups accounts by size, based on the number of employees. You can create a bucket column named Size on the Accounts report." This confirms bucketing as the correct method.