This means that the event or match related to that leg in your bet has been cancelled, abandoned or postponed for greater than 24 hours.
If the leg of your single bet is resulted as VOID, then your stake will be refunded.
If you have placed a multi with a leg that is resulted as VOID, your multi will remain LIVE and the odds contribution of the voided leg will revert to 1.00, when calculating the combined odds of the multi.
If you had a two leg multi bet and both legs had odds of 2.00. The combined odds of the multi would be 4.00 (2.00 x 2.00). If one legs becomes VOID, then the combined odds will revert to 2.00 (2.00 x 1.00).
If the remaining leg is resulted as a win you are paid out at the reduced odds (2.00), as one of the two legs has been voided.
If the remaining leg of your multi bet loses, then you will lose the multi bet, and your stake.