When you buy land or a place to live, you usually need to pay registration tax. This varies a lot from one country to another. In Belgium, this is quite high (10-13% - ish). You can get some discounts in some cases. Here are the links I've found:

The idea is that if your cadastre (yearly tax for habitation) is under a threshold you can be eligible to pay half of the registration fees. When you think the value of a house is usually over 300,000€ and the minimum tax is 10% of that, getting 5% back would actually mean 15,000€ (aka lots of money!)