How to describe "the remaining portion of a target" in a simple term or phrase?
Solution 1:
I can find no single word but such a target is sometimes referred to as a quota
Quota = fixed limit on the amount of something that someone is allowed to have or is expected to do:
Cambridge
The remaining part is referred to as the unfulfilled quota.
Examples are easy to find online. Here is one chosen at random:
In May, in its proposal to reform the Dublin asylum system, the commission said member states who do not accept to relocate asylum seekers would have to pay €250,000 per person in their unfulfilled quota.
euobserver