It is a system used by officials to review decisions made during a match.
For the first time, VAR was used in a major event in 2017 at the FIFA Confederations Cup. The Bundesliga and Serie A were the first of the world's major leagues to make the switch in the same year.
VAR was developed in the early 2010s by the Refereeing 2.0 project, which was led by the Royal Netherlands Football Association.
VAR examines the footage from as many angles as possible. In the beginning, real-time replays will be utilised to assess intensity. Slow-motion replays will be used to determine the point of contact.
When an offside is spotted, AI processes all player and ball data in real-time and sends an alert to the VAR. VAR must then confirm the accuracy of the kick point and offside line before informing the referee, who can confirm the decision.