Invisable seam in mittens

Hello
I am trying to figure that out " the invisable seam in mittens" I do not understand.

Could someone please help me

Are you reading a pattern? Can you tell us a little more about what it says?

What seam do you mean? Mittens knit in the round have no seam. :??

there is no pattern I am doing a 2 needle pattern and it does not say how to sew them>
knittingangel

You can check out the video on Mattress Stitch. It leaves a ridge on the inside, but is as invisible as it gets on the outside.