What does the term 'ripple carry' refer to in adders?

The term 'ripple carry' in the context of adders refers specifically to a delay encountered in the binary addition process due to the nature of how carries are propagated through a sequence of full adders. In a ripple carry adder, when adding two binary numbers, the carry-out from one full adder becomes the carry-in for the next full adder in the chain. This sequential handling means that each subsequent full adder must wait for the carry to be computed from the previous adder before it can complete its operation, leading to a delay in producing the final sum.

As the number of bits increases, the delay caused by ripple carries becomes more significant, because each full adder must sequentially wait for its predecessor. This is why ripple carry adders can be slower compared to other types of adders that use different methods of carry propagation, such as carry look-ahead adders, which can compute carries more rapidly.

In this regard, ripple carry is tied directly to the manner in which carries are handled during binary addition, confirming why the correct response relates to the delay caused by sequential input carry handling.