Pidgins often arise in wartime or sporadic trade situations as a lingua franca for the necessary communication. There is frequently a power differential involved.
In more long-term situations where groups speak different languages, such as colonization/occupation or slavery, a pidgin may evolve into a creole, which is considered a language unto itself.

A mixed language, or jargon, incorporating the vocabulary of one or more languages with a very simplified form of grammatical system of one of these and not used as the main language of any of its speakers.

Pidgins usually grow up in response to an economic need between either inhabitants of neighboring language-speaking regions that come in intimate contact, or between European traders and African/American/Asian cultures. Pidgins tend to take the easiest features of both languages and use them, rejecting any redundancy. Many pidgins exist such as West African language/English pidgins, French/Asian pidgins, and even a pidgin which has become an official language of Papua New Guinea, called Police Motu. It derives this name from the fact that the Papuan police force consisted of draftees from all around the island, where a multitude of languages are spoken, and they all had to communicate somehow. When a pidgin begins to develop complex grammatical forms and redundancy (which is almost universally necessary in language), and most importantly, becomes the mother tongue of a people, it is then called a creole.