De Morgan's Theorems:
De Morgan's First Theorem
It says that complement of sum equals the product of complements.
The LHS of the equation explain a NOR (NOT-OR) gate and the RHS of the equation explain an AND gate with inverted inputs and both of the equations have the same truth table as illustrated in Figure
Figure: (a) NOR Logic Gate, (b) AND Gate with Inverted Inputs, and (c) Truth Tble