"Cooperative purchasing", procurement conducted by, or on behalf of, more than 1 public procurement unit or by a public procurement unit with an external procurement activity.

"External procurement activity", (a) a public agency not located in the commonwealth which would qualify as a public procurement unit; (b) buying by the United States government.

"Local public procurement unit", (a) a public agency not located in the commonwealth which would qualify as a public procurement unit; (b) buying by the United States government.

"Public procurement unit", a local public procurement unit or a state public procurement unit. 

"State public procurement unit", the offices of the chief procurement officers and any other purchasing agency of the commonwealth or any other state.

A public procurement unit may participate in, sponsor, conduct or administer a cooperative purchasing agreement for the procurement of supplies with public procurement units or external procurement activities in accordance with an agreement entered into between the participants. The public procurement unit conducting the procurement of supplies shall do so in a manner that constitutes a full and open competition.