Alternating Current (AC) and Direct Current (DC) are two different ways for electric energy to be created and used.
AC has sinusoidal voltage and current with changing electromagnetic fields. DC has constant voltage and current with static electromagnetic fields.
The changing magnetic fields enables transformation to higher voltages for AC circuits. This advantage lead to AC circuits becoming the most prevalent circuits in the power grid, as well as our homes. DC circuits have found new life as a technology to reduce losses on very long bulk power transfers as High Voltage Direct Current (HVDC).