Teardown is the channel state between when the call is ended and either a)the channel gets reset for the next call, or b) the channel gets removed.
Channels in teardown are not supposed to hang around like that. This indicates that there's a problem in the code that is supposed to automatically remove those channels. If you find channels sitting in TEARDOWN state, you can right-click on the channel and choose 'Disable' to manually remove them.
Denny