|Definition - The modified version of the immigrant parents' language that is spoken by their children. For example, often, the children will speak the language fluently but will have a smaller and less sophisticated vocabulary than their parents.|
1. Shifting language use in some African cities has led to some young urban people growing up with "heritage language" levels (as described in your definition) of what are ostensibly "maternal languages." In one situation I observed, a Peace Corps volunteer spoke better second-language Hausa from 3 years in rural Niger than a Hausaphone employee of an agricultural research station!
(Don Osborn at bisharat.net)