An affinity diagram is a tool used to organize and group data. It is often used during brainstorming sessions to group sets of ideas or issues.
During the brainstorming session ideas and issues are annotated on pieces of paper or sticky notes and then grouped together organized by their relationships with each other. Once all issues have been captured and grouped the end result can be captured using a word processor or spreadsheet.
Affinity diagrams work best when organizing medium or large sets of data.