Nonstandard English is the option that describes the term "slang".
Slang is a type of language that consists of words and phrases regarded as very informal, nonstandard register, usually restricted to a particular group of people. Slang is most commoly used in speech rather than in written language because is not part of standard vocabulary.
The correct answer is nonstandard English.
By definition, slang is a type of language that is very informal. Its main characteristic is that is typically used by a certain group of people and in a specific context.
Another main characteristic is that slang is most commonly used in speech rather than in writing.