Trundle bed
A trundle bed is a low, wheeled bed that is stored under a normal bed and can be rolled out for use by visitors or as just another bed.
When pulled out, regular trundle beds remain at a height lower than the parent bed. However, pop-up variants also exist.
A pop-up trundle bed can be raised to meet the height of the normal bed, effectively creating a wider sleeping surface when positioned side-by-side. A lever on the side of the pop-up trundle is typically used to raise and lower a trundle bed.