Final answer:
A frank carious lesion is an advanced stage of tooth decay that is visible as a cavity in the tooth.
Step-by-step explanation:
A frank carious lesion is a term used in dentistry to describe an advanced stage of tooth decay. It is a visible and obvious cavity in the tooth that extends into the dentin, the layer beneath the enamel. This type of lesion is usually characterized by a yellowish or brownish color and can cause pain and sensitivity.