A void is when the property is empty and not generating any rent.
Landlords try to minimise void periods.
Many novice landlords who have been told that their buy-to-let property is worth €1500 per month, will then end up with it empty for three months only to then have to let it for €1300 per month.
It is much better for landlords to have a property let at the outset for a realistic rent. Once a void is experienced then a landlord will never get this money back. It is financially better to get €1300 for 12 months of the year than to get €1500 for 10 months (€15,600 versus €15,000).