A friend who you both enjoy each other's company and keep each other happy, but you both don't expect the friendship to last long. You both, however, always have each other's back and never back from a fight together. Considering how ugly trench warfare was, any friendships made were often broken by illness, artillery, gas, or gunfire. (never used during those times)
I really enjoy hanging out with him, but I feel he's more of a Trench Friend than a best friend
I have more Trench Friends than actual friends
by WardenMan May 9, 2018
The dreadful (yet metaphorical) place where a lady that takes a man's fancy resides when he forgets to kiss her goodbye after a date, or generally behaves in a way that will prevent said female from ever jumping into bed with him. Tell tale signs include introductions as 'some guy,' and gagging gestures whenever he tries to flirt.

To the average male, it is slightly worse the seventh circle of hell.
Dave: I think i've found myself a lovely, sexy, hot, female 'friend.' FUCK!
Andy: Why don't you just rag the shit out of her?
Dave: We're in the friend trench.
Andy: Ouch.

by fuelofbritain March 13, 2008