AC stands for ‘alternating current’ which means the current constantly changes direction. Mains electricity is an AC supply, and the UK mains supply is about 230 volts. It has a frequency of 50Hz (50 hertz), which means it changes direction and back again 50 times a second. It’s better for transporting current over long distances, which is why we use it for mains electricity.
DC stands for ‘direct current’ which means the current only flows in one direction. Batteries and electronic devices like TVs, computers and DVD players use DC electricity - once an AC current enters a device, it’s converted to DC. A typical battery supplies around 1.5 volts of DC.