If something is slatted, it has slats. Slats are long, thin, flat pieces of wood or metal.
Slatted things are often seen in old houses or on farms.
Examples:
The bed is slatted.
The slatted door lets in some air.
The slatted window is open.
The slatted fence keeps the animals in.
The slatted roof lets the sun in.
The slatted floor is cool on my feet.