Jitter is variation in timing rather than simply a consistently long delay. Network packets or media delivery can arrive less evenly under changing conditions, and playback systems use buffering to absorb some variation. Too much variation relative to the available buffer or real-time deadline can disrupt otherwise sufficient average data delivery to the viewing device.
A practical example
A connection may deliver enough data on average but pause briefly between bursts. A player's buffer can cover some irregular arrivals; if the interruption lasts longer than the stored playable content, the viewer may see a pause while it refills.
A common misunderstanding
Do not diagnose jitter from one isolated speed number. Timing variation needs appropriate measurements or repeated observations, and buffering can also result from other network, device or source problems.
Related terms
Stable technical definition. Editorial approach