A is for Alpha Centauri, whose human colonies were wiped out by the Xindi in the timeline of "Twilight"
B is for Bombing of the Earth Embassy on Vulcan
C is for Coalition of Planets, the proto-Federation beginning to form by series end.
D is for Denobula Triaxa, the home star system of the Denobulan race.
E is for T'Pol's Excellent bum.
F is for Football, AKA Soccer, still going strong in 2155
G is for Gavimetric sweet spot. Travis' favorite spot on the ship. Which he shared with Trip.
H is for Hoshi Sato
I is for the mid-22nd century Earth starship Intrepid, which helped repel the attack on Enterprise by Klingon Captain Duras.
J is for Jonathan Archer, captain of Earth's first long-range exploration vessel
K is for Klingons, first contact was made in the pilot.
L is for Lesser life forms, which the transdimensional Sphere Builders considered the inhabitants of the Delphic Expanse.
M is for matter conversion technology. As seen in use by the automated spacecraft repair facility.
N is for Nausicaan pirates...with more human-like mouthpieces than prior (later) Nausicaans.
O is for Orion slave traders, who are quite active in the Borderland near Klingon space.
P is for "Phwoar!" Reed uttered while admiring T'Pol's bum
Q is for Q who thankfully never appeared.
R is for the Roe-mu-lan Empire. Nope; it's pronounced Rom-u-lan
S is for Suliban
T is for the Tandarans.
U is for United