The first, flash (typically lowercased), has to do with the type of memory contained in a portable storage device. Flash memory -- sometimes referred to as solid-state memory -- has no moving parts. It's traditionally regarded as a safer means for data storage, but it's also more expensive.
The second, Flash, is a type of multimedia platform found on websites. You may become aware of it when a website fails to run on your screen and you're told you need to update your Flash player. Flash is used to run graphics and video and other types of moving images.
