Pop music may be distinguished from classical or art music and from folk music, but since the term spans many rock, hip hop, rhythm and blues (R&B), country, dance and operatic pop acts, it is reasonable to say that pop music is a loosely defined category.
Exclusive partner, more commonly known as an EP (pronounced E-P), is the stage in a relationship in which you have full exclusivity with another person, with the intention of pursuing a relationship in the near future. However, this other person is not your boyfriend/girlfriend yet.
EPUB is the same format used by the popular Stanza [free, iTunes link] app for iPhone and iPod touch. It's a free and open standard format created by the International Digital Publishing Forum (IDPF), and it's designed for reflowable content that can be optimized to whatever device is being used to read a book file.