When a person starts a posting on a message board, or forum, or Facebook, that others are able to comment on, that original posting and the comments on it are called a thread. A thread hijacking occurs when one or more individuals commenting on the original posting, go off topic, creating a separate conversation. This is rude, and bad internet etiquette . If people want to discuss a different topic, they should start their own thread.

Below is a thread, consisting of an original posting and comments on that original posting. They illustrate a thread hijacking original posting: I'm so excited that my cat has learned to use the toilet with City Kitty ! The training seemed like it took forever, but it's so worth it to not have to deal with a litter box any more! Has anyone else done this?comment 1: Ugh! I just started training my cat, but he can't seem to move beyond the orange stage. How'd you get through that?comment 2: I'm training my dog at PetCo classes. She's very smart. She learns the commands faster than the other dogs.comment 3: I'm training my dog in PetCo classes too. They have great trainers. They're patient with the dogs and the people.Comments 2 and 3 are off topic and are hijacking this thread. The person who made comment 2 should have started their own thread. The person who made comment 3 is guilty of continuing the hijacking.