Final answer:
A wet mare is a female horse that has recently given birth and is nursing her foal. The mare is known as 'wet' because she is lactating.
Step-by-step explanation:
A wet mare has foaled during the current breeding season and is nursing the foal. The correct term to describe a horse in this condition is c) Wet mare. Wet mare refers to a female horse, or mare, who has recently given birth and is currently producing milk to nurse her foal. This is in contrast to a maiden mare which has never been bred, an open mare which is not currently pregnant, and a broodmare which may or may not be nursing but is used primarily for breeding purposes.