A sidememe is a meme currently taking place that almost everyone knows about, but there is a bigger meme taking place at the same time which is getting more attention and is more popular. The sidememe is still popular, but is "second best" to the biggest meme currently taking place.

Internet persona(s) who happens to follow you and you happen to follow them back and maintain communication with and have a mutual liking for eachother whether it be friendship wise, etc. (Mutuals if more than one mutual)