You can picture the behavior of an OR operation with the switch model and register the result Q in the truth table...

In logic equations the operator \(\vee\) is used for the OR operation... $$Q = A \vee B$$ (Speaking: A or B). 
With the CMOS IC 4071, you build an OR operation...
Logical Sum Mathematically the OR operation is similar to the addition and is therefore also known as logical sum. Therefore, you will find variations of the logic equations... $$A \vee B \equiv A + B$$ 
Next the NOT operation...