What is the difference between a USB Flash drive and a thumb drive?

Alright USB is Universal Serial Bus wich is used to connect devices to your comptuer. Now a thumb drive is a very small device that has a varitey of the ammount of storage they can hold. Now Flash Drive sometimes reffered to as Thumb Drive is really fast but cost more and holds less. Now USB hard drives are slow transfer rate but the thumb drive plugs into a USB so im not sure what exactly you mean. Hope this helped :)