I got a bunch of the same response, so I guess I didn't ask the question clearly.
I'm well aware of how a short works. I was asking what parent poster had in mind when they said "if you think the market's going down, short it". Short what? Specific stocks? That's not the same thing as shorting "the market". When people say "buy the market" or whatever they're usually talking index funds or etc.
So did he mean some kind of leveraged inverse VFINX? Or a baroquely complex derivates ETF that's just a ticking time bomb like those inverse VIX funds from earlier this year?
Anyway, sorry for the late reply.