A trash bag or garbage bag was a solid bag used to dispose of trash.
While talking with Beckett Mariner about how the crew was surrounded by four Borg drones, Captain Amina Ramsey made an opinion about how they would smell like old trash bags. (LD: "Much Ado About Boimler")
While hallucinating, Sam Rutherford tried to warn Natasha Yar about Armus, saying that "the garbage bag's behind you!" (LD: "Veritas")