It means they have a rope, tendon or nerve at the top. It is the name of a group of snakes, usually aquatic (Name of the genus and belong to the family Acrochordidae ). They have a ventral fold that makes swimming easier.
Acrochordus : Genus of squamous sauropsides composed of primitive snakes found in Australia and Indonesia that are given the vulgar names of wart snakes, elephant horn snakes, dog-faced snakes or arafura snakes , among others.