Throughput is the amount of data a connection can move in a given time, usually measured in bits per second. In cyber security, it matters because encryption, inspection, tunneling, and filtering all add overhead that can reduce the usable data rate a device or network can sustain.
Low throughput can cause slow downloads, laggy remote access, choppy video, and delays in security tools that must process traffic in real time. In a VPN, for example, throughput affects whether encrypted traffic still supports smooth streaming or fast file transfers. Defenders watch throughput to size links, tune protocols, and detect bottlenecks, while attackers may try to overwhelm bandwidth to reduce service quality or create denial-of-service conditions.