Cokernel of Multiple Matrices

Question

Let $R$ be a commutative ring. Given an $m\times n$ matrix, $A$ over $R$, the cokernel of the matrix is the $R$-module $R^m/\text{Im}(A)$ where $A$ is viewed as an $R$-linear map from $R^n$ to $R^m$. However, I've come across an unfamiliar notation. Given two $m\times n$ matrices, $A$ and $B$, over $R$, what is meant by $\text{cok}(A,B)$? I encountered this notation in Leuschke and Wiegand's book on Cohen-Macaulay representations.