At Admin Panel -> Settings -> Switches, the "summaries" switch adds a prompt for people to type a short summary of their listing. This summary is in addition to, and shorter than, the regular full description. The summary is displayed in the category listings and search results, while the full description is displayed on the details page. If summaries are turned off, the full description is displayed everywhere. If you encourage submitters to make long and heavily formatted descriptions with images and such, you'll probably want to enable summaries to have a brief alternative.

When no summary is entered for a listing but summaries are on, the summary will be the description shortened to the summary maximum length and stripped of all formatting.