Jitter is a significant performance metric in networked systems, affecting real-time applications like VoIP and video conferencing. It refers to the variation in the time delay between data packets over a network, typically measured in milliseconds. Causes of jitter include network congestion, route changes, or improper queuing. Jitter can be mitigated using jitter buffers or optimized network configurations. The impact of jitter on real-time audio and video communications can be significant, as these applications are highly sensitive to timing inconsistencies.