A full adder is a digital circuit that performs the addition of three binary digits: two significant bits and a carry bit from a previous addition. It produces two outputs: a sum and a carry-out. The sum represents the result of the addition, while the carry-out indicates whether the addition resulted in a value that exceeds the binary digit limit. Full adders are essential components in arithmetic logic units and are often used in constructing more complex circuits like ripple carry adders. They can be combined in groups to add multi-bit binary numbers, making them fundamental in computer architecture and digital electronics.