What do we call a language that is derived from multiple languages, like English?

The term that describes a language derived from multiple languages is "pidgin." A pidgin language typically arises in contexts where speakers of different native languages need to communicate, such as in trade or colonial settings. Pidgin incorporates elements from various languages but has limited vocabulary and simplified grammar, creating a functional means of communication without being a fully developed language.

In contrast, a creole is a stable, fully developed language that evolves from a pidgin when it becomes the first language of a community, often featuring a complex structure and a robust vocabulary. A polyglot refers to a person who knows and uses several languages, while a dialect refers to a variety of a language characterized by specific vocabulary, grammar, and pronunciation used by a particular group.

Hence, the most appropriate term for a language derived from multiple languages, like English, is "pidgin."