Kind of, Sort of, and Type of

The expressions kind of, sort of, and type of are essentially interchangeable:

a certain kind of person = a certain sort of person = a certain type of person

Remember not to add an article (a or an) at the end of this expression:

a kind of a person
a kind of person

Remember to keep number consistent in phrases using these expressions:

this kind of environments
these kind of environments

this kind of environment (all singular)
these kinds of environments (all plural)

This rule has not always been followed, and the usage “these kind of [noun]s” has a long, well-established history. However, this usage is now generally considered nonstandard.

The use of kind of and sort of as an adverb meaning somewhat (“kind of cool”) is considered slang. However, you only need to avoid this usage in formal writing.