This lecture covers the concept of a full adder, a fundamental component in digital electronics used for binary addition. The instructor begins by explaining the structure of a full adder, which consists of three inputs: two binary digits and a carry-in. The lecture details how the full adder computes the sum and carry-out values based on these inputs. The instructor presents the truth table for the full adder, illustrating how different combinations of inputs yield specific outputs. The design of the full adder is discussed, including the use of PMOS and NMOS transistors, highlighting the number of transistors involved in the circuit. The instructor emphasizes the importance of understanding the carry logic and how it affects the addition process. Various cases are analyzed to demonstrate how the full adder operates under different input conditions. The lecture concludes with a summary of the full adder's functionality and its significance in constructing more complex arithmetic circuits.