Knit to "M"?

I am making hedgehog mittens, which can be found here:

I am on the thumb portion, at the end part. It says:
K2tog, K to M, ssk, K to M

However, I don’t know what the M stands for. It’s confusing me. Thank you!

In the second paragraph under Thumb you placed a marker (PM). Now the instructions want you to knit to the Marker (M), ssk, K to Marker.