Chain and Loop Selection

Detects if there is a set of contiguous edges within a solid or mesh object, or within or between surface The chain may either be open or closed and is available in the SURFPATCH, SURFBLEND, MESHCAP, and FILLETEDGE commands

Chain 

Chain option identifies and fillets edges that have continuity

This part does not have rounded corners so the fillet operation is limited to the selected edge

This part has rounded corners enabling the Chain option to select and fillet all the continuous edges

Loop

A loop is similar to a closed chain
After selecting an edge, you can choose which of the potential loops to use