Regiment

A regmient is a military unit that in size and organisation is typically between a battalion and a brigade.

Cardassian Union
A khesharo was the Cardassian equivalent to a regiment and was made up of around 5,000 soldiers commanded by a gul. 

Dominion
A regiment in the Dominion is comprised of three battalions numbering 2,187 Jem'Hadar and commanded by a Chelek'atorn. 

Romulan Star Empire
A lagor'val is the Romulan equivalent to a regiment and was formed around a group of tresh'val (battalions) and was between 8,000 - 12,000 soldiers with a colonel in command. 

Starfleet Ground Forces
A Starfleet Ground Forces regiment is between 1,500 and 5,000 Starfleet soldiers (two to five battalions) and is typically commanded by a major or colonel. (LUG RPG: )