From UFStarfleet Wiki
A runabout is the designation of a type of vessel smaller than a starship but larger than a shuttlecraft. Runabouts are equipped with limited weapons and drive systems, but offer additional living space and the ability to be configured to mission-specific cargo capacities. They have a larger operational range and better weapons capability compared to shuttles, and are capable of speeds of up to warp 5. Runabouts are typically assigned to space stations or starships as auxiliary craft.
The Danube-class of runabouts entered service in 2368, and remain the most common type of runabout in servoce with Starfleet.