Are files encrypted with gpg compatible with pgp? What about the other way? I recently learned the very basics of the procedures of using gpg to encrypt and decrypt files. But I don't have a lot of knowledge or good understanding of cryptology theory. I also hear about pgp. Besides the obvious and confusing -- at least to me -- resemblance of the name of one to the other, are the two system compatible with each other?
Yes, both GnuPG and the commercial PGP.com are implementations of the same OpenPGP standard; in fact, GnuPG was specifically designed to be PGP-compatible.
The only differences you might encounter are:
tl;dr: Yes, they are compatible.