The colloquial usage of non-standard words, commonly used by "ghetto" and "hip" individuals. Slang is notorious for degrading the quality of a language, but yet also evolves it. In fact, most of the words you and I use were probably not in the first dictionary.
However, slang does not mean to sell drugs. Many think that in Dem Franchize Boyz song "White Tee", they reference drug trafficking using the word "slang" (I bang in my white tee, I slang in my white tee). Rather, slang (verb) mean to front
someone by using slang words to insult them, and "bang" referring to gangbanging.
Modern language would be horrendously incomplete without slang.
Italian, Spanish, French, Portuguese, and Romanian are all slang versions of Latin