As far as sexual slang goes, the term "glory hole" makes it seem like you've entered into a realm where you've won the jackpot. And, in a way, you might have -- depending on which "end" of the hole you found yourself.
Its origins are funny and it's not unlikely for you to actually encounter one -- depending on where you like to hang out.
The term "glory hole", as with most sexual innuendo, comes with a double meaning. Originally, the term referred to a "surface depression in underground mining". For petroleum production, it's a kind of underwater excavation. Especially in the context of petroleum production, the term is pretty positive because it serves up major economic gains. And this is probably where the sexual term evolves from.
It is essentially a hole bored into the partition walls of a lavatory stall so individuals on either side can engage in sexual activity. This could include the penetration of the rectum with fingers or the insertion of a penis anally, vaginally or to receive a blow job.
Glory holes are quite eroticized not only because of their anonymity and almost voyeuristic behavior but also because both individuals can explore each other sexually without ever revealing any other physical compatibility. Neither party, in short, feels judged and the only thing that exists is the sexual pleasure and excitement. That in itself can be arousing.
It was a practice that was very much used by gay males in gay sexual culture in order to engage in erotic, anonymous, especially in social settings. Because gay clubs, bars and other venues were havens for closeted gay and LGBTQ individuals, they were an erotic (and useful!) way to "get some" and "get off" without ever having to reveal themselves.
However, many social theorists caution that people's motivations and experiences when engaging with them vary. Many proponents of pornography focus on filming the anonymity and certain sense of trespassing that it provides.
Meanwhile, many individuals also feel that using the "holes" to engage in sexual activity allows one party to depersonalize the penetration and sexual act by focusing only on the "hole" and so the individual is simply an object of desire, instead of being perceived as a complex person.
The ensuing HIV-pandemic is not the only concern with glory holes and their use. Public toilets and stalls that are used are frequented by many individuals, with varying levels of personal hygiene and other afflictions that could be present.
While the practice itself is worthy of eroticizing, the obvious health risks are huge, especially in an uncontrolled environment. There is at least some etiquette involved when using a glory hole. For example, individuals doing the insertion must wait for a signal from their anonymous partner to say that they're "ready", so that there's no bodily injury or rough sex.
Glory holes often appear at clubs, lounges and raves, where public sex happens often -- though it's still illegal.