The log line is the idea of your story – not the entire story in one sentence.
On this page are links to other pages to help you to better think about developing log lines for your project.
Log lines are the ultimate branding and/or marketing tool: one sentence descriptions with a hook to capture attention. But they are not branding which is slightly, markedly different.
Use loglines in selling your cinematic ideas; use them in life. In this way life and cinema are interchangeable! — PT
http://www.movieoutline.com/articles/writing-good-log-lines.html
Wait! What’s the difference between a logline and a tagline?
I am glad you asked! It’s the difference between telling and selling your story.
“A log line or logline is a brief (usually one-sentence) summary of a television program, film, or book that states the central conflict of the story, often providing both a synopsis of the story’s plot, and an emotional “hook” to stimulate interest. A one-sentence program summary in TV Guide is a log line.” — Wikipedia (contains examples)
Log Line courtesy of the United States Navel Academy