It means it has multiple meanings. Someone who is lesbian(me) could say I’m gay if someone asked cuz it means I love the same as myself(gay umbrella term definition). If a person also doesn’t like specific labels they can also decide to just use the word gay. Trans is also an umbrella term, it’s like a tree. The umbrella term is the tree itself(trans), but all the branches are specific things(genderqueer, non-binary, trans-masc, agender, etc)
I don't know which country you're from, but in mine, gay only means men who have relationships with men. It's not an umbrella term here. Queer would be the umbrella term. That's why I found it strange, in fact, as a pansexual, I find it extremely annoying when people name bisexual and pansexual characters as gay, I really feel like they are ignoring the existence of other sexual orientations. Anyway, my comments, both this and the other, are just rants.
Why is everyone saying "you're gay too"? He's not gay. He can be bisexual or pansexual, but not gay or straight. Why do you keep acting as if bisexuals and pansexuals don't exist? It's tiring ( ̄へ ̄)