The definition for data consistency is:

"A policy that specifies or describes how up-to-date an
instance of data is in one service of a distributed system,
with respect to one or more instances of that data
elsewhere in the system."

I would expect a policy to define the requirements for consistency, and/or to specify the rules for determining whether 
a given data set is consistent w.r.t. some other data set, while data consistency would be an indication of whether a 
data set conforms to a given policy.  So this definition seems more like a definition of "data consistency policy".