What is the difference between a memory card and a memory stick?

Memory Stick (note capitals) is a Sony brand name for a memory device used mostly in Sony cameras, it is vey flat in shape, almost like a small Chewing Gum stick. A flash drive is a USB device, I'm sure you know what one looks like. Many people say memory stick when they mean flash drive, because flash drives are somewhat stick shaped. Another term for flash drive is 'pen drive'.