A gate is defined as a digital circuit which follows some logical relationship between the input and output voltages. It is a digital circuit which either allows a signal to pass through as stop, it is called a gate.
The Logic Gates are building blocks at digital electronics. They are used in digital electronics to change on voltage level (input voltage) into another (output voltage) according to some logical statement relating them.
A logic gate may have one or more inputs, but it has only one output. The relationship between the possible values of input and output voltage is expressed in the form of a table called truth table or table of combinations.
Truth table of a Logic Gates is a table that shows all the input and output possibilities for the logic gate.
George Boole in 1980 invented a different kind of algebra based on binary nature at the logic, this algebra of logic called BOOLEAN ALGEBRA. A logical statement can have only two values, such as HIGH/LOW, ON/OFF, CLOSED/OPEN, YES/NO, TRUE/FALSE, CONDUCTING/NON-CONDUCTING etc. The two values of logic statements one denoted by the binary number 1 and 0. The binary number 1 is used to denote the HIGH value. The logical statements that logic gates follow are called Boolean expressions.