Latency is the delay between a request and its response, such as the time between pressing a key and the character appearing, or between sending audio and hearing it. It is measured in milliseconds or smaller units.
In practice
Musicians recording through a USB audio interface notice latency as a lag between playing a note and hearing it in headphones. Audio drivers designed for low latency use smaller buffers, shortening the delay at the cost of more processor work.
Common confusion
Latency is not bandwidth. A connection can carry a great deal of data per second yet still respond slowly to each request. Wireless devices typically add latency compared with wired ones, though modern designs reduce the difference considerably.
Why it matters to readers
Drivers influence latency through buffering and how quickly they respond to interrupts. Release notes mentioning reduced latency usually concern audio, input or networking, where small delays are most noticeable.
A closer look
Latency accumulates across many stages: the device itself, the bus, the driver's buffering, the operating system's scheduling and the application. Improving one stage helps only if it was a large share of the total. That is why audio professionals measure end-to-end round-trip latency rather than relying on any single number from a specification sheet.
