This cable is used between the handset and base unit of telephones, or fax machines fitted with handsets. Fitted with a standard RJ10 plug at each end.
A note regarding the quoted length:
Specifying a length for a 'stretchy' cable is clearly difficult. The length quoted is the overall length of the cable before it is coiled as part of the manufacturing process. In use, when fully extended (stretched) it reaches about 70% of the length quoted. When not stretched it is approx 15-20% of the length quoted.