Kinktionary
More like guidelines and a lot less like definitions.
Gloryhole
A sexual act where there is a wall with a hole between the participants of the activity. In many cases the interaction will be a blowjob, however any sexual act with a penis or phallic shaped object going through the hole is possible. In some cases hands or fingers may also be used through the hole to sexually stimulate the other person. The term Gloryhole refers to the hole in the wall.
Originally something that was found in public lavatories by people making holes in the walls between stalls it later evolved to being purpose built in places like sex cinema's or sex video arcades. It is very much associated with gay male culture as clandestine encounters were previously the norm. The first documented occurrence of a gloryhole comes from 1707 in a court case and it was later used in the mid 1900s as an entrapment method to catch gay men (source).
In some cases a gloryhole may be box or booth where multiple people can make use of the same person inside. The anonymity of the interaction is in many cases something that is desired and adds to the experience so there are also specific set ups for this that offer an experience where you will not see the person on the other side at all.
Gloryholes can be used by people of all genders. The hole can be used to access mouths, genitals, ass, boobs, and everything.
For alternative anonymous interactions people can also use a fuckbox, this is sometimes found in the same places as a gloryhole.