A is for Alpha Centauri.
B is for Betazoid.
C is for Cardassia III.
D is for Denobulus.
E is for Earth, capital and central planet of the Federation.
F is for Ferenginarn.
G is for Gorn eyes. Some had silvery compound ones, others had more reptillian ones with irises and pupils.
H is for Holographic testicles.
I is for Irradiated. If you stood too close to an unshielded warp reactor, this could happen to you.
J is for Jadzia Dax.
K is for Kamarag, Klingon Ambassador to the Federation from at least 2286 until at least 2293.
L is for Ligon II.
M is for Martian Colonies. At least one existed before the year 2067 and full colonization was considered to have been achieved by 2103.