Don't take the term's name as its definition.
Example: Pillow shading does not mean to shade pixel art with a pillow-y texture but rather to shade it as crap. Or something. >.>
EDIT: Actually, it's more like it's a homebrew since it was all made at home while hacks use games. So hacks aren't entirely made at home. Erm. Erm. Like Serio said, a homebrew is made from the ground up. Though I wouldn't say completely since a lot of them use ripped sprites and music.