Wiktionary
matrix management
n. A type of organizational management in which people with similar skills are pooled for work assignments and may have more than one manager.
Wikipedia
Matrix management
Strictly speaking, matrix management is the practice of managing individuals with more than one reporting line (in a matrix organization structure), but it is also commonly used to describe managing cross functional, cross business group and other forms of working that cross the traditional vertical business units – often silos - of function and geography.