A dock line is used to attach a boat to a dock. It is generally among the thickest and sturdiest lines on board.
A dock line is used to immobilize a boat at a dock. However, such a line also can be used for other purposes: lashing, towing, etc.
The two variables of a dock line are its constituent material and its configuration. It can be made of natural fibers (hemp, cotton, etc.) or synthetic material (nylon, polypropylene, etc.) It can be laid or woven of different strands and filaments in a variety of patterns. The flexibility and breaking strength of the line will depend on these factors.
Choice will depend on type and size of craft. Elasticity and breaking strength also should be considered.