Accounting Dictionary:

Activity Center

Pool of costs of two or more activities.

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Activity centre is a term used in urban planning and design for a mixed-use urban area where there is a concentration of commercial and other land uses. For example, the central business districts of cities (CBD) are also known as 'central actvities districts' (CAD) in recognition of the fact that commercial functions are not the only things that do or should occur there. The term activity centre can also be used to designate an area for mixed-use development, whatever its current land use happens to be.
Wikipedia article "Activity centre".