Portuguese overseas exploration in the 15th and 16th centuries led to the establishment of a Portuguese Empire with trading posts, forts and colonies in Africa, Asia and the Americas. Contact between the Portuguese language and native languages gave rise to many Portuguese-based pidgins, used as linguas francas throughout the Portuguese sphere of influence. In time, many of these pidgins were nativized, becoming new stable creole languages.
As is the rule in most creoles, the lexicon of these languages can be traced to the parent languages, usually with predominance of Portuguese; while the grammar is mostly original and unique to each creole with little resemblance to the syntax of Portuguese or the substrate language.
These creoles are (or were) spoken mostly by communities of descendants of Portuguese, natives, and sometimes other peoples from the Portuguese colonial empire.
Until recently creoles were considered "degenerate" dialects of Portuguese unworthy of attention. As a consequence, there is little documentation on the details of their formation. Since the 20th century, increased study of creoles by linguists led to several theories being advanced. The monogenetic theory of pidgins assumes that some type of pidgin language — dubbed West African Pidgin Portuguese — based on Portuguese was spoken from the 15th to 18th centuries in the forts established by the Portuguese on the West African coast. This variety was the starting point of all the pidgin and creole languages. This would explain to some extent why Portuguese lexical items can be found in many creoles, but more importantly, it would account for the numerous grammatical similarities shared by such languages, such as the preposition na, meaning "in" and/or "on", which would come from the Portuguese contraction na meaning "in the" (feminine singular).
Origin of the name
The Portuguese word for "creole" is crioulo, which derives from the verb criar ("to raise", "to bring up") and a suffix -oulo of debated origin. Originally the word was used to distinguish the members of any ethnic group who were born and raised in the colonies from those who were born in their homeland. In Africa it was often applied to locally born people of (wholly or partly) Portuguese descent, as opposed to those born in Portugal; whereas in Brazil it was also used to distinguish locally born black people of African descent from those who had been brought from Africa as slaves.
In time, however, this generic sense was lost, and the word crioulo or its derivatives (like "Creole" and its equivalents in other languages) became the name of several specific Upper Guinean communities and their languages: the Guinean people and their Kriol language, Cape Verdean people and their Kriolu language, all of which still today have very vigorous use, suppressing the importance of official standard Portuguese.