Final answer:
A linear crack in the skin extending into the dermis is known as a stretch mark. Stretch marks occur when the dermis is stretched beyond its elastic limits, often due to rapid growth or weight gain.
Step-by-step explanation:
A linear crack in the skin extending into the dermis is known as a stretch mark. Stretch marks occur when the dermis is stretched beyond its elastic limits, often due to rapid growth or weight gain. They typically have a reddish color initially but fade over time.