Displays the excerpt of the current post after applying several filters to it including auto-p formatting which turns double line-breaks into HTML paragraphs. It uses get_the_excerpt() to first generate a trimmed-down version of the full post content should there not be an explicit excerpt for the post.
The trimmed-down version contains a ‘more’ tag at the end which by default is the […] or “hellip” symbol. A user-supplied excerpt is NOT by default given such a symbol. To add it, you must either modify the raw $post->post_excerpt manually in your template before calling the_excerpt(), add a filter for ‘get_the_excerpt’ with a priority lower than 10, or add a filter for ‘wp_trim_excerpt’ (comparing the first and second parameter, because a user-supplied excerpt does not get altered in any way by this function).