node disjoint

Routes SXD, SYD, and SZD in  have no links or nodes in common and are therefore node disjoint.

link disjoint

Routes SXYZD and SYD in (b) have node Y in common and are therefore only link disjoint.

non-disjoint

Routes SXD and SXYD in (c) have node X and link SX in common and are therefore non-disjoint.

 

finally 😀 😀 😀