If this variable is nil, no threading will be done, and all of the rest of the variables here will have no effect. Turning threading off will speed group selection up a bit, but it is sure to make reading slower and more awkward.

If non-nil, all threads will be hidden when the summary buffer is generated.

All threads that have a total score (as defined by gnus-thread-score-function) less than this number will be expunged. This variable is nil by default, which means that no threads are expunged.

if you kill a thread and this variable is non-nil, the subtree will be hidden.

Sometimes somebody changes the subject in the middle of a thread. If this variable is non-nil, the subject change is ignored. If it is nil, which is the default, a change in the subject will result in a new thread.

This is a number that says how much each sub-thread should be indented. The default is 4.