It's old LGB slang. And I use that shortened version of LGBTQ to illustrate how old the slang term is, not to exclude anyone

Back before gay marriage here in the US became legal, there was even less acceptance for people that weren't pure hetero. So, sometimes, folks would have a fake partner. Often, it was a lesbian and a gay man paired up to cover each other. But it could also be a friend, or even just someone hired for a specific event.

Staying in the closet at work was not too difficult, but family? That was a lot harder. So, having a boyfriend or girlfriend made it relatively easier to keep things quiet. A beard was the fake hetero partner.

In our case, I played the role for both of them, as needed. But it was usually only one of them that needed it. The other was pretty "butch", and put was only extended family that weren't aware of their orientation. Most of the time, it was just showing up to family gatherings, pretending to be dating. Every now and then it would be something a bit more complicated, but that's tangential.

So, yeah, it is kinda like filling a seat at public events :)