chBT stands for "Channel Bittorrent
", and is a way of identifying within a conversation, how you viewed/acquired a tv episode that may not have been released on free to air television in your city/region.
Person 1: got the latest episode of Lost off chBT last night.
Person 2: Cool, don't ruin it for me though, because I've just been watching it on free to air, and we are a month behind.
Person 1: No worries.