Which term is synonymous with a birthmark or freckle?

The term that is synonymous with a birthmark or freckle is "macule." A macule is a flat, distinct, discolored area of skin that is not elevated, meaning it does not protrude above the surface of the surrounding skin. Macules are typically small and can vary in color and form; both birthmarks and freckles are types of macules.

In terms of other options, while a lesion refers to any abnormal change in the structure of an organ or part due to injury or disease, it is a broader term that can encompass various types of skin irregularities, including macules but is not specifically synonymous with them. A pustule is a small blister or pimple that contains pus, often related to infections or inflammatory skin conditions, which is quite different from the characteristics associated with birthmarks and freckles. A scar represents a mark left on the skin after a wound or injury has healed, again differing significantly from the nature of a macule.

Thus, "macule" is the most precise term that describes characteristics of both birthmarks and freckles, making it the correct answer.