When we say “Rate,” what we actually mean is “Interest Rate.”
Simply, this is the cost you pay for borrowing money. Your mortgage lender takes a risk by giving you money, so they charge interest on the loan to make the risk worth it. That interest is a percentage of the loan amount that you pay on top of your principle.
For the most part, rates move with financial markets (specifically, the bond market) and the economy. However, every client receives a custom rate specific to their situation.