Fiber usually means fiber-optic cabling: strands of glass or plastic that carry data as light. It is used for backbone links, data centers, telecom networks, and long-distance connections because it offers very high throughput, low latency, and resistance to electrical interference.
In cyber security, fiber matters because network security is also physical security. Attackers may try to cut, tap, or damage fiber routes to cause outages, intercept traffic, or force failover paths. Defenders rely on route diversity, locked conduits, intrusion monitoring, and redundant links to keep services available. Even when the cable itself is hard to exploit, weak provisioning or poor labeling can let an insider or intruder reroute traffic, so fiber protection is part of both resilience and access control.