What does dimension in integer programing problem mean

Question

In the problem P1 below described in a research paper I am reading, the authors say that the problem P1 below is a three dimensional integer programing programing problem. Can I ask what does 3-dimension means here? does it mean that it has three min/max functions or three or the fact that it depends on three variables $a\in A, n\in N,$ and $, m \in M$.

Explanation of Problem P1

Answer 1

It is a 3D problem because you have three variables here, $n, m, k$.