Skylights in the simplest explanation is that portion of the house or building that is covered with a transparent covering that allows the light from the outside enter the space and keep out the other elements like rain and snow. This feature of the building provides natural lighting into the space inside.
There are different materials that skylights are made from but the most common is glass and plastic. It is usually installed at the portion of the roof that is why it is also called a roof window. Skylights can also be installed at the side of the building or at the walls.