What is it?
The best answer is to look at this discussion to see what it was intended to be, then read the commentary below the tf script (link below) to see what it actually became and why.
In short, it's a separate 'window' (or, in the case of tf, 'window section') which supports streaming data from the MUSH for a 'realtime' display of basically whatever you want.
There is one significant restriction, based on tf limitations: it can only be up to 6 lines high.
Because of this (in an attempt to cooperate with tf defaults for the 'status line'), the scripts contained herein voluntarily limit themselves even further, by leaving 'line 0' alone (line 0 == the default status line in tf) ... further reducing their capacity to 5 or fewer lines.
Without providing actual screenshots, I think that's about the best I can give for a brief description of these pages.