It is a host it yourself website for Universities. It provides a way for teachers to provide lecture notes, give assignments, accept submissions, post grades, have a message board. All of the features are access controlled so only students in the class can see assignments, you only see your grades, etc.

Only it isn't done very well, and the company has a patent on using a website to manage a classroom or some such BS. So they sue rather than fix it.

A corporation; here, it's meant to refer to the Blackboard Learning System, which is Blackboard's course management software. Students can log in and view assignments, readings, etc. that faculty post.

It's closed source and <opinion> a colossal pain in the ass to use.</opinion> The institution I work at recently switched away from it to Moodle, which is the big open-source alternative (which, in the interest of full disclosure, I think is pretty great).

It's a company that pretty much owns the education market, despite their products being nearly universally considered to be harmful^H^H^H^H^H^H^Hhorrible.

For more information, see wikipedia: http://en.wikipedia.org/wiki/Blackboard_Inc

Edit: I should point out that my knowledge of blackboard is near non-existant, I haven't had to use it in any of my schooling (university in central florida, public education in silicon valley), so I don't have a useful opinion of it.