DIT stands for Details in Thread. This is commonly used in Total Fark threads where a TFer further explains a situation detailed in the headline.
Headline: I lost my dog, DIT.
DIT: So I'm a terrible person and a bad dog owner. I left the door open to take out the trash and the dog ran out. He's a black lab. I haven't seen him in three hours now. I'm too lazy to put up fliers and post in craigslist. Any local farkers, can you keep an eye out for him?
Anon-DIT is for people who have deeply personal issues to discuss and can't afford a therapist and/or trolls. These people will post usually lengthy description of their problem and ask for help. Instead of the details being in the thread and showing who posted, Anon-DIT instead is put in the link field, ensuring anonymity.