Since this is urban dictionary, I'll give the more modern definition:
Of or relating to a subculture which developed in the late 70's as an offshoot of punk, characterized by unconventional hairstyles and clothing. Originates from a musical style which is still alive to a certain extent, gothic rock artists include Bauhaus, She Wants Revenge (more recent), and Sisters of Mercy. The term gothic comes from a 19th century literary style, which is the basis of horror fiction. As a general term, gothic means dark.
Stereotypes surround the gothic subculture, like any other subculture, including an association with Satanism (coming from a false connection between atheism and Satanism), a belief that goths (or gothics, to distinguish them from the Germanic tribe) dress unconventionally to attract attention from mainstream culture, and an association with depression and evil. Dark themes are what characterize gothic music and literature (also film and television), and these fictional themes are often misapplied to people. However, some of the negative stereotypes surrounding gothic culture are a result of (excuse my bias here) assholes who pretend to be vampires, cut Marilyn Manson into their backs with knives before going to a concert, and other attention-seeking shock artists who give the impression that gothic culture is about celebrating all things gruesome and barbaric. (Not that I have anything against a little violence in entertainment)
This is very cliche on urbandictionary, but here are some things that are not gothic"
Self-harm or suicide (although depression is a common trait in youth regardless of subcultural orientation, and the lead singer of the early gothic music group Joy Division committed suicide)
Pretending to be a vampire.....outside of Halloween, that's just ridiculous
Gothic music: see above
Gothic movies: almost anything related to Dracula, Frankenstein, vampires
Gothic clothing: this varies from subspecies (excuse my terminology) to subspecies of goth, including cybergoth, romantic goth (old school), heavy metal goth, "mallgoth" (an insult applied to goths who embrace gothic fashion and culture for reasons perceived to be superficial, however, some of this is just elitism), etc