Which description fits a nodule in dermatology?

The defining characteristic of a nodule in dermatology is that it is a solid, palpable lesion that typically exceeds 0.5 cm in diameter. This assurance of being palpable—and often elevated—distinguishes it from other skin lesions. Nodules can vary in shape but are generally rounded, and they can be located in the dermis or subcutaneous tissue.

The other descriptions provided do not accurately match the clinical definition of a nodule. For instance, a flat lesion larger than 0.5 cm may describe a plaque or patch rather than a nodule. Similarly, a fluid-filled lesion that is 0.5 cm or less likely refers to a vesicle or bulla rather than something solid like a nodule. Lastly, a lesion that is elevated but only 0.5 cm or less would typically be characterized as a papule, not a nodule. Thus, option B correctly aligns with the established dermatological criteria for identifying a nodule.