What do you understand by truth table and Boolean expression?

Explanation

Truth table. It is a table that shows all possible input combination and the corresponding output combinations for a given logic gate. It is also called a table of combination.
Boolean expression. It is an expression invented by Georga Boole which deals with logical combination of inputs and outputs for a given logic gate.
The Boolean expression for OR gate is `A+B=y`, indicates that y equals A OR B. Here symbol plus(+) is referred to as OR.
The Boolean expression for AND gate is , `A.B=y`, indicates that y equals A AND B. Here symbol dot (*) is referred to as AND.
The Boolen expression for NOT gate is `barA=y`, indicates that y equals NOT A or A negated. Here symbol bar over Ameans we change A to the alternative digit i.e. `bar(1)=0` and `bar(0)=1`