Suckfic is a term used to name the genre of bad fanfiction. Sucky fiction is then shortened to suckfic. Suckfics are known for bad grammer, bad spelling, M-preg, Mary Sue/Gary Stu/Marty Stu, random Japanese insertions, and blob ellipses.
Fanfiction: And harry looked up at mary sue and said hi mary..........then mary...
Reader: What the? Mary Sue? Where are the quotation marks? This is a suckfic?