Decreolization is a process of homogenization a creole language may undergo when in contact with one of its parent languages, particularly if the parent language is ascribed a prestige value. To put it another way, in decreolization, the influence of the superstrate language dismantles influences from substrate languages.
If one views pidginization as a process of simplification, reduction, and admixture from substrate languages, and creolization as the expansion of the language to combat reduction, then one would view decreolization as an attack on both simplification and admixture.
As languages remain in contact over time, they inevitably influence one another. Typically, the language with higher prestige (most often the lingua franca) will exert a much greater influence on the lower prestige language (the creole). This leads to the reintroduction of complexities, irregularities and redundancies into the creole from the source language. Elements of other sources begin to disappear as there is less and less linguistic territory for them to cover. It is theorized that eventually the creole will resemble the source language to such a degree that it can then be called a dialect of that language rather than a separate language at all.
Another name for a near-fully decreolized language is a “vestigial post-creole.”
Jamaican Creole, which exists in continuum with Jamaican English and Standard English, Jamaican Creole is much more akin to standard English than most other English-based creole languages. Also, the creole is recognized by Jamaicans as “bad English,” the more standard varieties being more common in educated and urban settings, so there is conscious effort made to alter the speech of poorer, rural folk towards the English norm.