A language isolate is a language that does not have another language related to it.
Many languages are related to other languages, because they both come from an older language, and are similar to other languages. These groups that are similar are called language families. Most languages belong to a language family, but some are not related to other languages. These languages are called language isolates.
Some language isolates are Basque, and Zuni language, Erina language and Burushaski.