What is 's?
1.
How the grammatically-challenged make a noun plural.
Look at all these definition's.
2.
Added to the end of a word to make a singular possesive (or sometimes a plural possesive with words whose plurals do not end with S, such as people) or a contraction with "is" or "has". Poorly-educated people/foreigners tend to use it for plurals and verbs, but that usage is incorrect.
-Correct-
Bob's cat is black.
Bob's going to the store.
Bob's gone to the store to get his cat some food.
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-Incorrect-
Cat's are fluffy animals.
Bob has a cat that overeat's.
