terminology - What is the difference between a point-and-shoot and a mirrorless?

Both point-and-shoot camera and mirrorless cameras seems to be mostly similar in the way they work.

So, What are the differences between a point and shoot and a mirrorless camera?

Is a mirrorless camera a point-and-shoot with big sensor, an electronic viewfinder and interchangable lens? If so, why call it a whole new product variety?