A is for Apollo. For a god. He wasn't very smart.
B is for Beta Quadrant. Most of the Klingon and Romulan Empires were located within its boundaries.
C is for Chekov. He screams a lot.
D is for Delta Vega. Galactic edge or near Vulcan. Take your pick.
E is for Epsilon Indi.
F is for French starship captains.
G is for Gobbledegook. Actors who appear regularly in Star Trek must be fluent in it.
H is for Harnessing the power created by matter-antimatter annihilation to travel faster than light.
I is for Iconian gateways. Which go even faster.
J is for James Tiberius Kirk.
K is for Koloth, commanding officer of the IKS Gr'oth around 2267 and 2268.
L is for latinum. The motivation behind all Ferengi.
M is for Martian colonists from Earth.
N is for neutronium. Worth it's weight in latinum. Maybe.
O is for Odona of the planet Gideon.
P is for photonic lifeforms. Aka holograms.
Q is for Q, the mate of Q and mother of Q who was almost a victim of the civil war inside the Q Continuum.
R is for Romulan Bird of Prey.
S is for Sand. More than a few worlds encountered during the long annals of Starfleet exploratory history were covered in this.
T is for Troi's catsuits.