There are two types of electrical current flow; direct current (DC) and alternating current (AC).
DC flows in one direction only and is the primary type of current used in logic and control circuits.
AC alternates in polarity, flowing back and forth, and is the main type of current found in household electrical mains.
AC is the typical current used to power appliances, and is often converted to DC within an appliance to power the logic circuit boards.
Mapping the polarity of household AC over time reveals a sine wave, but it may also have other waveforms.
AC is described by its period (cycle time), frequency (cycles per second, measured in hertz (hz)), and amplitude (magnitude of waveform measured in volts).