A is for Assimilation. Achieved through means of nanoprobes.
B is for Beard. Presumably, no Borg has one. (Anything to avoid saying the obvious 'Borg')
C is for Cube, their ships are.
D is for Delta Quadrant, the primary residence of the collective.
E is for Eye, you can count on one of them being replaced or enhanced.
F is for FULL REVERSE! Often yelled by the XO of a starship once the Borg has it within a tractor beam. (note: it never works)
G is for Green. The color of Borg cutting beams.
H is for Humanoid, which all Borg seem to be.
I is for Icheb, once a drone, not always a drone.
J is for Jeri Ryan, who played another former drone.
K is for Killing Federation starships at Wolf 359.
L is for Locutus, Resistance is futile....Numbah One.
M is for Mammaries. Seven of Nine had them.
N is for Nanoprobes. Produced by the trillions.
O is for Omega Molecule, or Particle 010. They want it.
P is for Prosthetic Enhancements, the Borg have plenty.
Q is once again for Q. If the Borg somehow assimilated one, it'd be quite a big problem.
R is for Resistance. It is futile.
S is for Species 8472, arguably the Collective's greatest enemy.
T is for Transwarp Conduit.
U is for Unimatrix Zero.