gel
1. A substance, resembling petroleum jelly in viscosity, that surrounds a fiber, or multiple fibers, enclosed in a loose buffer tube.
Note: This gel serves to lubricate and support the fibers in the buffer tube. It also prevents water intrusion in the event the buffer tube is breached. [FAA]
2. Index-matching material in the form of a gel. [FAA] Synonyms index-matching gel, matching gel.