“An excerpt is a condensed description of your blog post and refers to the summary entered in the Excerpt field of the Write Post SubPanel […] The excerpt is used to describe your post in RSS feeds and is typically used in displaying search results. The excerpt is sometimes used in displaying the Archives and Category views of your posts. […] An excerpt should not be confused with the teaser which refers to the first few sentences or paragraphs of a post. ”

Wordpress Codex