Tumblr is known for its insular culture, hatred of outsiders and “nerds”, and love of dark irony. The slang of Tumblr largely centers on reactions to others’ content, especially negative ones.
Knowing these terms is essential to “breaking in” to Tumblr, as otherwise a new user will be swiftly ejected from the online society. Playing “by the rules” is a must in this monocultural community.
What is air?: A response signaling extreme emotion or appreciation. The implication is that the subject of the reply is so amazing, the reader can’t remember merely “great” things like the French electropop band Air. The first person to ask it was Photoshopped into an advice meme: