It is Balance:

(1) the act of monitoring a budget and making sure you do not over or under spend.

(2) the maintenance of proportions, a correct ratio of resource types, reflecting the mission of the fund, as well as built-in flexibility to deal with inflationary increases and other contingencies.

It should reflect needs of Departments & other Constituents

and 

follow Collection Development Policies.

To find out, see Budget Analysis Reports.