Laptop's require AC adapters (alternating current) to convert power available in a home or office to DC (direct current). An AC power adapter plugs into the laptop's DC jack. It is called the DC jack because it only accepts DC.
A DC connector (or DC plug, for one common type of connector) is an electrical connector for supplying direct current (DC) power.
Compared to domestic AC power plugs and sockets, DC connectors have many more standard types that are not interchangeable. The dimensions and arrangement of DC connectors can be chosen to prevent accidental interconnection of incompatible sources and loads. Types vary from small coaxial connectors used to power portable electronic devices from AC adapters, to connectors used for automotive accessories and for battery packs in portable equipment.