A split-king or dual king mattress comes in two pieces rather than one. Each piece is about the size of a twin-sized mattress. A split-king sheet comes with two fitted sheets, one for each of the two twin-sized mattresses.
A typical king bed is the widest standard size on the market. It usually measures 76 inches from side to side. A split-king mattress allows two people to share a bed without having to share a mattress. This allows both to have a mattress with their preferred firmness. Dual kings also reduce motion transfer, allowing less disruption from one person's restless sleep.