What's an excerpt? According to the Typepad Knowledge Base:
The Excerpt field can be used to generate a short summary of your blog post. If you do not write an excerpt yourself, one will be generated automatically from the first 100 words of the post or the number of words you have set in Settings > Posts & Pages, under Auto-Generated Excerpt Length.
The excerpt for a post is used when sending a TrackBack and/or in your feed if you have selected Short Excerpts under Feed Content in Settings > Feeds.
The excerpt will also be used as the Meta Description for the individual post.
As part of The Essential Solution®, IMS provides suggested excerpt copy with each week's blog content. This excerpt appears at the top of each blog post and should be customized to your own voice. Once edits are made, simply highlight copy and paste this excerpt into the proper field when composing your blog post. You will find the excerpt field at the very bottom of the Compose New Post page.
The excerpt should not be duplicated in the body of the blog post.