An elastic cord was a type of string known for its elasticity.
In 2450 of an alternate timeline in which Benjamin Sisko , while speaking to Melanie about his temporally displaced father, Jake Sisko compared his connection with Benjamin to an elastic cord, saying, "It was as if he was frozen in time at the moment of the accident, and the link between us was like an elastic cord. Every so often the cord would go taut enough to yank him forward into my time. But only for a few minutes. I realized that if my motion through time came to a stop, the cord would go slack and he'd be lost in subspace forever. But if I could cut the cord when the link was at its strongest, while we were together, he'd return to the moment of the accident." (DS9: "The Visitor")