You MAY be thinking of this technique. I take it your referring to yourself too. Anal stimulation on a woman in addition to anal sensitivity can include deep penetration so her ASpot is being poked and this usually leads to massive orgasms just like GSPOT G-GASMS.
It is done DURING masturbation or a good blow job and sometimes during regular intercourse. It is a unique feel and enhances (usually and if your partner knows what they're doing) and can prolong the feeling of make orgasm. It means stimulating the prostate which is a GLAND so you have to start off VERY gently or you'll think somebody manage to boot you there. Usually our O's last 2 and a half seconds. This can sort of slow down the feeling and stretch it over 30 minutes or so and then you have a normal orgasm and that feels like your head may explode at the same time.