Well, yes, there is a difference; as described in [man]features.file-upload.post-method[/man]; [font=monospace]name[/font] is the name the file the user had given it before uploading it. But the server saves all uploaded files in a temp directory until you (through your application) decide what to do with them, and if two people upload a file called "bike.png" at the same time then one would trash the other. Not good. So the server saves each file in the temp directory with a distinct temporary name that won't clash with any already in the temp directory. That name is provided to you in the [font=monospace]tmp_name[/font] field.
HTML5 does offer a "multiple" setting for its file input fields, but HTML 4 didn't, and I don't know if the developers have got around to updating PHP's handling (since the page dalecosp and NogDog link to don't mention anything about it, in the absence of anything else in the manual to the contrary, I'll surmise not).