When you're talking about more than one, you're talking about multiple things. A machine with many fixtures has multiple parts. A person that seems like two totally different people on different days might have multiple personalities.
The word multiple comes from the Latin multiplus meaning "manifold." When something exists in multiple forms, it's manifold, or has many kinds. Think of a multiplex theater that can show multiple movies at once. Walk through a garden full of flowers and you'll see multiple kinds of blooms. A multiple is also a number that can be divided into another number without a remainder. Multiples of five, for example are ten, fifteen, twenty... — you get the picture.