diff --git a/doc/_info_/tctyp.order b/doc/_info_/tctyp.order
index 1d9d8d98..4bb142ae 100755
--- a/doc/_info_/tctyp.order
+++ b/doc/_info_/tctyp.order
@@ -380,7 +380,8 @@ TIMLAC		Like SIMLAC except that the Imlac is a PDS1 and cannot
 TISILENT	Declares the terminal to be an older TI terminal (TI 72X
 		or 73X).  The 740 series is better declared with a PADCR 0.
 
-TT2500		Declares the terminal to be a TT 2500.  What is this?
+TT2500		Declares the terminal to be a TT 2500, which is the
+		Marvin Minsky's Turtle Terminal.
 
 TTYNUMBER <n>	Tells TCTYP to deal with some other
 		terminal than its device TTY:.