"siendo" is the gerund of "ser": to be. maybe it is used a lot in latinamerica as a "loan" expression of the wide used of gerund in english, but it is not very usual y iberic spanish. por ejemplo, se puede decir: "sigue siendo mi amigo"= he is still my friend, or "por ese precio sigue siendo muy caro"= this price is still too expensive. most usual is the use of the adverb "todavia/aun. ex: "todavia es mi amigo" and "ese precio todavia/aun es muy caro". the meaning of both phrases in the examples are the same and the last ones sound not vulgar. (at least in spain).