A BS-ay, as it's name says, is an essay that has been bullshitted the whole way through yet somehow still manages to make sense. It is basically the main difference between high school and college essay writing. High school=essays. College (especially community college)= BS-ays
HS Student: I hate essays
College Student: We don't write essays in college. We write BS-ays
HSS: What's a BS-ay?
CS: It's an essay that's been bullshitted all the way through and miraculously still makes sense