tar is not a compression program per se, but a file archiving tool. It is used because it preserves file system information such as permissions, owner and group, which would otherwise be lost if you used zip/gzip/bzip alone. Each letter has a meaning, x is for extract, f is file, v is verbose (print details to screen) and f is for file. So the cryptic four letters are really easy to rememeber: eXtract the Zip File Verbosely. Change the x for a c (Create) and you can make a new file.