Yeah, I know this is a really noob'ish question.
Anyway, I've been downloading TV show episodes in HD from iTunes and got to wondering if my 2011 iMac even shows content in true HD. I don't know much about display resolutions, but does the iMac actually show content in 720 or 1080p when you watch an HD video? If not, then can I presume that Airplay streaming via Apple TV on my HDTV shows the content in HD?