What is deepsea fishing line called?

There are several forms of line used in deepsea fishing. Monofilament is used but will stretch 20% or more so it is difficult to get a good hook set into a fish. It is also sensitive to the UV component of light and needs to be washed frequently. It has a life of one caught fish to one year, depending on use and storage.

Dacron is a woven line. It has little stretch (1-4%, depending on manufacturer) and is relatively bulky.

Spectra, also called Dyneema, braid or superline) is also a woven line. Made of extruded fibers, it is very thin for it's strength and has almost no stretch. It is taking over the deep drop market due to it's increased sensitivity and great strength. It requires better knots due to its slippery surface.