What is depression =/ ?

for a while i thought i was depressed... because i felt bad all of the time, but i know why i feel bad, and i might have that same reason to feel bad forever, i dont think that should mean i will always be depressed... more of a drawback, something i will never be happy about... i started looking up all different types of depression and all the symptoms, tons of names, initials and other weird medical words to describe me... so i was thinking =/ maybe its just something i feel bad about, i hate to use the term "depressed" or any other medical term to describe myself... like bi polar or something... i suppose i just decided not to consider myself depressed anymore... because on the surface i think a lot of people look happy.. fake smiles occasionally =]... i think everybody must have something that drives them crazy, really annoys them and they wish they could change... does that mean we are all "depressed"? GAH... i dont want to think of myself as depressed, where are the borderlines of it, how bad do you have to feel and for how long before it changes from a bad feeling to depression?