Throwing shade is a subtle way of disrespecting or ridiculing someone verbally or nonverbally. Shade also calls up, and may likely be taken from, the slang adjective shady, characterizing something or someone as “weird” and “dumb” since the 19th century, evolving to “questionable” or “objectionable” in decades since. While the phrase received some attention in major newspapers in the 1990s–2000s, it went mainstream in part thanks to its appearance in 2010 on an episode of RuPaul’s Drag Race involving a fiery exchange of disparagement.

Source: Dictionary