A class of drug (Selective Serotonin Reputake Inhibitor) designed to 'treat' depression, though there is no real evidence that these drugs work beyond temporary stimulation, numbing, placebo effect, or a combination of such. Remember, the 'treatment' of mental illness is highly subjective and is not well understood, making it an easy gray area to screw around with for profit. The 'clinical results' have been fudged by the pharmaceutical companies (who test the drugs themselves) and the FDA, and what little reliable information left obfuscated by nondescript language and misrepresentation. There are many dangerous side effects which have been reported, and are also underplayed purposely to boost sales. In reality, we understand very little about the nature of Serotonin and the brain, so giving SSRI's to 'depressed' patients is simply a stab in the dark to avoid dealing with real issues at hand.
Depressed? It can't be because you feel helpless in a world where the only real choices available to work for a dispassionate corporation or suffer on the street. It can't be because you never felt connected to anyone. It can't be because you were abused at home! No! It's biological! I swear! I'm a real scientist, and I'm just pulling shit out of my ass, but my white lab coat and nondescript brain scan means I'm right! Seriously! Here, take these potentially dangerous and useless drugs! They're called SSRI's! And you really need to want it to help, because that's the only way it will! Wait it's just a placebo effect, but don't tell anyone, and if you do I'll give you more drugs to help treat your 'problems with authority'.
Selective Serotonin Reuptake Inhibitor - a 'class' (different 'classes' treat different things) of antidepressant medication.
Prozac, Zoloft and Lexapro are all SSRI's.