A is for Alpha Centauri, one of the very first interstellar colonization destinations for humans from Earth.
B is for Bajor. Somehow a strategically important planet populated with a bunch of annoying people.
C is for Cryogenically frozen supermen.
D is for Delta Vega. That planet really gets around.
E is for Elim Garak. A tailor, spy, and all around pretty cool guy.
F is for Flag of the Federation.