An interest rate is the rate at which interest is paid by *any* borrower for the use of money that they borrow from a lender.
That borrower could be *you* borrowing money from *your bank* (in the form of a loan). Or, if you are filthy rich, the borrower could the *the bank* borrowing money *from you* (in the form of savings accounts, for example).
But... why is one interest rate different from another? Part of the reason is how much control over the money you let other people have over your money, and for how long.
Let's say I have $1000 in my savings account, but I can go to the bank and withdraw it anytime I want. I'm not going to get a very high interest rate on that -- because the bank can't loan it out to other people and make money on it.
But let's say I have $1,000,000 in the bank, and I tell the bank "you can freeze my $1,000,000 for a whole year -- I can't touch it. You can do whatever you want with it." I'm going to make a lot more money off of that -- because the bank will be able to loan my $1,000,000 out as car loans, house mortgages, education loans...