Latency
Short definition
Latency, in virtual reality, is the delay between a head movement and the corresponding update of the image in the headset.
In plain language
If the image is slow to follow the head, what the eyes see no longer matches what the inner ear senses, and this can cause discomfort. For this reason, VR systems aim to keep this delay very low, in the order of milliseconds. In a session with an older or frail person, high latency can be a reason to stop.