A flash drive (also called thumb drive, or USB drive) is pretty universal portable media storage. It's used for storage, often to transfer files between computers. Flash drives aren't specific to laptops or desktops, and are usually transferable between Windows PC and Macs.
1/500 of a GB... I've written a 5 page essay that was only a few hundred KB... Do the Math:
1024 KB in 1 MB
1024MB in 1 GB
So if my essay were 500 pages, that would be like 30,000-50,000KB which translates to roughly 20-50MB... 20MB is about 1/500 of a GB.