A “logline” is a movie’s concept boiled down to one or two sentences:
On his deathbed, a father tells the story of his life the way he remembers it: full of wild, impossible exaggerations. His grown son tries to separate the truth from the fantasy before it’s too late.
A “tagline” is a short, clever one-off found on a movie’s poster:
An adventure as big as life itself.
A logline can be thought of as the shortest possible pitch of a movie — what a writer could use to sell an idea to a buyer in just a sentence or two. Taglines are used by marketing departments to sell movies to audiences.