Take Out The Trash is a medal given after killing 500 enemies. This medal is not limited only for the campaign. Bots from side missions, daily missions, quickmatches, and squad codes also count as enemies.
One 'kill' required to make progress for this medal only counts if the player controls the soldier. Kills by AI team-mates that appear marked on the screen (spectacted by the player) do not count.
Even if the player quits a match, defeated enemies in that match do count as progress in the process of unlocking this medal.