Excerpt is usually the post summary in WordPress. It is being displayed to the reader on the main page of a WordPress Blog. After reading the post summary or excerpt, the reader can get the idea of what the post is about. 

Excerpt is to be written in a field given below in the posts editor. If you can not find the Excerpt field option, then click on the “Screen Options” on the top right corner and select the checkbox “Excerpt”.

You have a golden chance to engage more visitors by writing an attractive post summary and add into the Excerpt field. If Excerpt is empty, WordPress automatically creates an excerpt using the first 55 words of the post.