Garn Pattern - What is MT?

Hi everyone.

I am working on mittens [first mittens and colorwork project for me] and am not sure what is meant by MT in the bolded line in the example below.

I am thinking maybe - marker thread? But I am not sure. I tried Google search, looked at charts, and also searched the forum.

Pattern: Snowflake Mittens and Sweater.
Link to pattern [British English]:

Part of pattern I am confused about:

Work next round as follows: M.4, 17 (21) sts of M.6 (upper hand), M.4, 17 (21) sts of M.5 [B](insert a MT in transition between M.5 and M.4 to mark thumb)[/B]. When piece measures 1 cm inc 1 st on both sides of MT a total of 6 times on every 3rd round = 56 (64) sts – incorporate inc sts in M.5 as you go along.

thank you.


It does sound like it means to place a marker.