Structural analog

A structural analog, or analog, is a compound that has a structure similar to that of another compound, but one of the components is different.
That which is different (between two analogs), can be that one or more atoms, functional groups, or substructures, are replaced with other atoms, groups, or substructures. 
Structural analogs are often isoelectronic (or often have the same structure (positions and connectivities among atoms) and the same electron configurations, but are different by what specific elements are at certain locations in the structure.)