LIBERALS AND THE LEFT: Porphyrogenitus does a pretty good explaining the difference between the two (be sure to read his previous post on the subject). It helps to explain why we mostly use the term “leftists” around here, rather than the more common–and usually misapplied–“liberal”.
(And of course, there’s classical liberalism, but that’s actually the forerunner to today’s conservatism–not the FDR New Dealer-style liberalism that dominated the country prior to the new left of the Vietnam-era late-’60s and ’70s. Google some of Jonah Goldberg’s previous G-Files–he’s written extensively about this sort of terminology.)
UPDATE: Speaking of the left, Edward Feser has some thoughts on why universities are so dominated by them, in Tech Central Station.