Circuit is a closed path followed or capable of being followed by an electric current.
Electric Current is the directional movement of electrons between atoms in another words the flow of electrons through a circuit. It is measured in amperes or amps.
Alternating Current (AC): The direction of current flowing in a circuit is constantly being reversed back and forth. This means the direction of the current changes sixty times every second. Frequencies of 60 cycles per second (60 Hertz) are used for domestic and commercial power, but frequencies of around 100 million cycles per second (100 megahertz) are used in television. This comes from power plants that are operated by the electric company.
Direct Current (DC): Electricity flowing in a constant direction, and/or possessing a voltage with constant polarity. DC is the kind of electricity made by a battery (with definite positive and negative terminals), or the kind of charge generated by rubbing certain types of materials against each other.