>>519643780
It means lol.
The actual meaning is grass, but through a series of events it became jap slang for lol. If I remember right it comes from laughing (笑う, warau) shortened to w, and when spammed as wwwwww, like lolololol, a bunch of w:s kinda look like grass which led to 草生える (kusa haeru, grass is growing), and then it was finally shortened to just 草.