Hmmm, you listed two different acronyms in your question. but here goes:
FAT stands for File Allocation Table-- the topic you would hear that in reference to most often would be the file system that is used in older Windows operating systems called FAT32. Long story short, it's a format for storing computer data.
FTP stands for File Transfer Protocol, and it's a means for transferring files from one computer to another over the internet.
Maybe I'll write a hub about this if you need more information :)