If you did not understand the answer in Spanish here it is. No they are not slang. Nos is the reflexive pronoun for nosotros or nosotras And in certain countries they use vos to replace Tú as the pronoun. Spain and Argentina are two country's where vos is regularly used.

No. Nos es el pronombre reflexivo de nosotros. En algunos dialectos del español se usa vos en lugar de "tú", pero no significa que sea slang.