A shanty town, squatter area or squatter settlement is a settlement of improvised buildings known as shanties or shacks, typically made of materials such as mud and wood. A typical shanty town is squatted and in the beginning lacks adequate infrastructure, including proper sanitation, safe water supply, electricity and street drainage. Over time, shanty towns can develop their infrastructure and even change into middle class neighbourhoods. They can be small informal settlements or they can house millions of people.