It's a device that has a slot for the memory stick (or compact flash or whatever type of memory you have or even sometimes all of the above) that plugs into the USB port on your pc so you take the memory card out of the camera and pop it into the reader that acts like a drive for your computer so you can transfer images. I have one for my pc and my dad has a slot built into his laptop so whenever he needs a file that I have, I transfer it to the memory stick & bring it to him so he can upload it to his pc - it's easier than burning the data to a cd and more economical if there isn't enough to fill an entire disc.