The "excerpt field" is the short summary of your blog article.
Think of it as a teaser - like in a magazine, where an article's title and a short description is shown, followed by the page number.
Entering an excerpt to your blog post is very important - it gives your readers a glimpse of what the article is about when they see the summary. These excerpts are often shown on your website homepage, as well as on the list of recent blog posts.
For instructions on how to insert excerpts please click here.