This is 'hello' in Simlish. Simlish is the language that Sims speak. Whilst playing The Sims 2 or The Sims 3, when Sims greet each other they say 'sul sul'.

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)