A "sticky mat" is a kind of mat that has a sticky surface. It is commonly used to clean dirt and dust off of shoes or wheels before entering a clean area. Full definition
If your raised foot tends to slide down the inner standing thigh, put a folded sticky mat between the raised - foot sole and the standing inner thigh. (yogajournal.com)
But why not just use a regular sticky mat? (health.com)
Have her stand at your knees, bend forward, and place her hands on your top thighs, which can be padded with a folded sticky mat. (yogajournal.com)