Hollow-core is a type of precast, prestressed concrete

Prestressed concrete

Prestressed concrete is a method for overcoming concrete's natural weakness in tension. It can be used to produce beams, floors or bridges with a longer span than is practical with ordinary reinforced concrete...

 floor slab. It is often used in construction of multi-storey buildings. The advantages it has over a poured concrete floor are that it is lighter in weight and often cheaper. Also, wet concrete needs to be pumped or carried up to higher floors. The slabs which are manufactured off site are simply lifted with a crane

Crane (machine)

A crane is a type of machine, generally equipped with a hoist, wire ropes or chains, and sheaves, that can be used both to lift and lower materials and to move them horizontally. It uses one or more simple machines to create mechanical advantage and thus move loads beyond the normal capability of...

and set in place. Disadvantages are an increased overall floor thickness (due to the requirement of steel supporting beams), the cost of a steel frame over the cost of concrete columns and increased cranage requirements.