Creating Elite Sleep.....
Trundle beds (or truckle beds) are usually considered a pair of beds, one slightly smaller than a twin bed that is on rollers or casters so that it may be put beneath the upper twin bed for storage. Trundle beds allow for two separate beds to be available when necessary, but do not require the space constantly. It is a space-saving idea
source:http://en.wikipedia.org/wiki/Trundle_bed
Choosing Trundle Beds: The Beds Underneath
Choosing a trundle bed can be a great choice for a number of reasons.