Quick Definition: A story or topic started based on any subject matter (by the PUA or someone else), which becomes the main topic of the conversation in a group.
When people converse—especially strangers—they tend to focus on one specific thread and then give comments, insights, and feelings related to that subject. They move from one thread to another, or moving between threads.
Good friends talk about multiple threads, based on whatever comes to mind. Thus, a subtle way to build rapport with someone is to talk to them and switch naturally between subjects as if one was talking to their friend.
Time to start a new thread.