Small hemp rope or cord, in the region of four to five millimetres in diameter, used for lashings and so forth. I wish I knew why it is called Hambro line, though. Codline is technically not the same, but yachtsmen treat it as if it were, and either can be used for odd jobs. If not sure what to call cord when aboard, the term ‘small stuff will mark you down as a mariner of unrivalled experience, and saves you the trouble of searching for the precise term.