What does OCC on the website fanfiction mean?

OCC is a typing error, but there are two common abbreviations similar to it.

OOC stands for Out Of Character, and is when a character is acting very differently to how they normally do. It's usually quite annoying to read, but sometimes it works (if there is an explanation for the difference in behaviour)

OC stands for original character. This is a character who was invented by the author and is not present in the original material. OCs can be good or bad depending on the author, but generally work better as minor characters.