MMAO stands for "Mixed Martial Arts Orgy." This is a specific type of adult video that combines the themes of mixed martial arts, often involving fighters from various disciplines (like boxing, wrestling, judo, Brazilian jiu-jitsu, etc.), with group sex or orgies.
In these videos, participants may engage in both physical combat and explicit sexual activities, either as separate scenes or combined within the same video. The appeal of this tag is for viewers who enjoy the excitement of martial arts coupled with the eroticism of group sex or other fetishes.
As for "33," it could be an identifier for a specific series or just a random number assigned to the video by the creator. It doesn't have any specific meaning in this context.