The word borrow means to take something and use it temporarily. You can borrow a book from the library, or borrow twenty bucks from your mom, or even borrow an idea from your friend.
Usually , borrow implies taking something temporarily and returning it later. However, you can borrow non-physical things and adopt them as your own. For example, the English language has borrowed many words from other languages — such as Latin and Greek — but those words were never "given back." If you're subtracting numbers, you might have to borrow from the tens column to complete the problem.