The only dumb questions are the ones you don't ask @Captain24 I like to think! Always happy to provide some knowledge if I got it hehe.
Erasure is like... pretending that they don't exist. Like bi erasure is really common in films and tv - one example in Buffy for instance is that Willow is very happily dating Oz, then later on when she's with Tara she has a line where she says "Hello, gay now" implying she was never attracted to Oz (and even worse, that she somehow changed from straight to gay) rather than just saying 'I'm bisexual'.
Ace erasure is more that it's so rarely represented that people are surprised to learn that it exists at all! And there's some awful people who will think that an ace person just 'hasn't had good enough sex' or something horrible like that. So yeah, not just not accepted (though that is also an issue) but fully having our existence refused to even be acknowledged.
I think we're looking to change that, to create spaces that are specific to certain groups - so that all our lil queer folks have a space to feel safe and accepted. Cos unfortunately, being queer frequently goes hand in hand with having mental health struggles. Something about being targeted, discriminated against, ostracised, erased, and told that we're an affront to god, results in us having larger numbers represented in mh statistics, who could've guessed?