Network latency affects internet performance by introducing delays in data transmission between devices. Measured in milliseconds, latency can be caused by distance, congestion, or suboptimal routing. High latency results in slower page loads, buffering during streaming, and lag in online gaming, negatively impacting user experiences. Conversely, low latency ensures smooth interactions and quick responses in real-time applications. Reducing latency is crucial for enhancing overall performance, especially for services that require instantaneous communication and data transfer.