In science fiction, a shuttle is a small spaceship designed for transporting personnel and equipment between larger starships or between a starship and a planetary surface. Some types may have some form of FTL drive for inter-planetary or even inter-stellar travel as well. They also may or may not be armed.
Shuttles in Star Wars
The Empire used Lambda-class shuttles to carry passengers and small amounts of cargo on various routes: ship to ship, ship to planet, and planet to planet. The Lambda-class seems to be distinguished from starships primarily by its size, as it is fully capable of interstellar journeys using its hyperdrive. Shuttles of similar design were in use in the Old Republic, as well.
Shuttles in Star Trek
Nearly all Starfleet capital ships and starbases carry a complement of shuttlecraft.