salt lick

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A natural deposit of exposed salt that animals lick.
• noun A block of salt, often with added minerals or vitamins, set out for animals such as cattle, horses, sheep, or deer to lick.

from The Century Dictionary.

• noun A place resorted to by animals for the purpose of satisfying the natural craving for salt.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A block of salt, often enriched with other minerals, licked by herd animals to supplement their diet.
• noun A natural source of such minerals licked by animals.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a salt deposit that animals regularly lick