Loan payment terms- "Borrower will pay loan in full upon demand"

Is it normal for payment terms to require the following; "Borrower will pay this loan in full immediately upon lenders demand."? It follows with "If no demand is made borrow will pay this loan in 359 payments." This is an in house loan from a small local bank for a duplex I purchased. The terms of payment all make sense to me except the option that the bank could demand full payment at any time.  

Thanks for any knowledgeable advice!