[1] A glass filament cable that is used to transmit digital signals in the form of light.

[2] Optical fiber: a very long, narrow, flexible piece of glass. Used for high-speed communications.

Sources: [1] DEC Network Buyer's Guide 1992/93 Glossary

[2] BIG-LAN Digest, Volume 5, Number 67, Friday, November 5, 1993