Ansel allows you to store additional information about your images to allow them to be more easily searched and grouped. This information is stored in Ansel’s database and XMP sidecar files and can also be included within exported images.
Metadata (e.g. title, description) is free-format text that usually differs for each image. You can add metadata to images in the metadata editor module.
Tags are usually shared between multiple images and are used to categorise and group them. You can add tags to images in the tagging module.