This page contains information regarding Star Trek: Lower Decks, and thus may contain spoilers.
An away mission was a mission during which an away team, such as a landing party or boarding party, performed tasks in locations outside of their starship or starbase. This included missions on planetary surfaces and other starships. Away missions ranged from exploration or first contact to combat. The majority of these missions were launched using a ship's transporter to send the crew to their destination. When use of the transporter was dangerous or impossible, shuttlecraft were used.
Starfleet had several regulations and guidelines concerning away missions. While during the 23rd century, it was commonplace for a ship's captain to lead away missions, in the 24th century, this was discouraged in favor of having the first officer lead the away team. This new regulation did not prevent captains from joining all away team missions, however. For example, Captain Kathryn Janeway was part of the team that stole a transwarp coil from a Borg sphere and led the rescue mission into the heart of Borg territory, personally rescuing Seven of Nine. (VOY: "Dark Frontier") Several years later, Captain Jean-Luc Picard insisted on joining the away team which found B-4, as he was "itching to try out the Argo." (Star Trek Nemesis) Picard also joined an away mission to investigate an alien species using triolic waves, following Guinan's enigmatic warning that "If you don't go on this mission, we'll never meet." (TNG: "Time's Arrow")
Crew were normally not assigned to away missions if they were unable to pass certain proficiency requirements. As of 2376, Crewman Celes of the USS Voyager had never served on an away mission despite the vessel's having been stranded in the Delta Quadrant for over five years, due to being unable to pass these requirements. Two other crewmen on the ship, Mortimer Harren and William Telfer, had also never served on away missions, Harren due to never volunteering and Telfer due to being a hypochondriac and always getting an excuse note from The Doctor. This changed that year when Captain Janeway decided to mentor the group and assigned them to an away mission. (VOY: "Good Shepherd")