What does the term "addition reaction" refer to in organic chemistry?

In organic chemistry, an addition reaction refers specifically to a process where two molecules combine to form a single product. This type of reaction typically involves unsaturated compounds, such as alkenes or alkynes, which have double or triple bonds. During the reaction, these multiple bonds are broken, and new atoms or groups are added to the carbon framework, resulting in the formation of a saturated product.

This definition captures the essence of addition reactions, which are key in synthesizing more complex organic molecules from simpler ones. Hence, the choice highlighting the combination of two molecules into a single product accurately describes the fundamental nature of addition reactions.