A new blog post on the Star Wars: The Old Republic site lays out the forthcoming Legacy Achievement system that will arrive with the Scum & Villainy update. As with any achievement system, players can earn special badges and titles. Setting this particular one apart, however, allows all characters in a player's legacy to participate in earning achievements.
[A]ctions from all characters in your Legacy contribute to your Legacy Achievements. Need to discover and dance with 100 kinds of womp rats on Tatooine? No sweat---dance with 50 of them with your Scoundrel while he is on the planet and then go dance with the other 50 later with your Powertech. Your progress is tracked across both characters and the Achievement and its rewards are available to all characters in your Legacy. So you are always contributing to the same set of Achievements and rewards regardless of which character you are playing.
Read the full developer blog on the Star Wars: The Old Republic site.