A logic gate is an elementary building block of a digital circuit. Most logic gates have two inputs and one output. At any given moment, every terminal is in one of the two binary conditions low (0) or high (1), represented by different voltage levels.
There are seven logic gates: AND, OR, XOR, NOT, NAND, NOR, and XNOR.
The three most used gates are AND ,OR ,NOT.
OR: The OR gate gets its name from the fact that it behaves after the fashion of the logical inclusive «or.» The output is «true» if either or both of the inputs are «true.» If both inputs are «false,» then the output is «false.»