Is Word the Sheep A Abstract Noun?

No, the Word 'sheep' is a noun, a Word for a type of animal, a Word for a thing.

A pronoun is a Word that takes the place of a noun in a sentence.

Example: Why did the sheep cross the road? Because it wanted to get to the other side! (the pronoun 'it' takes the place of the noun 'sheep' in the second sentence)