An Irish woman. A woman with thick legs is said to be like a Munster heifer; i.e. beef to the heels.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Munster Plums * MurderNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes