Slang is informal language that is not necessary for natural speech and does not include dialects or pronunciation differences. Some common English slang terms described in the document include "to hang out" which means to spend time together, "to chill" which means to relax, and "hyped up" which means excited or enthusiastic about something. Other slang terms explained are "busted" meaning caught doing something wrong, "to have a blast" meaning to have a really good time, and "geek" or "geeky" meaning someone who enjoys studying. The document also provides examples of slang terms like "to be hooked on something" meaning to really like or enjoy something, "is it still a thing?"