This is a horses equivalent of a orgasm. In some hick towns in America where sleeping with animals is accepted, boasting in the bar about giving your horse a "Maregasm" is quite common and completely acceptable.
Cletis: I gone and got me a new horse called Betsie, She's a beauty, it took me a while but i gave her a "Maregasm" she aint never gonna forget!
John Boy: Way ta go Cletis, you a lucky man!
John Boy: Way ta go Cletis, you a lucky man!
by Paul Fleming July 14, 2006
The best gift you can give your marefriend. It is when your marefriend backs up into you and you cause her to climax
I celebrated my 2 year anniversary with my marefriend by grooming her, feeding her apples and eating out her sweet hay vagina until she had a maregasm
by marefriend May 4, 2015