What is this abbreviation?

I am knitting a princess crown pattern. I am just starting the crown and came across an abbreviation that I am not familiar with. It is sp2po. What is that?! How do I do it?

Slip 1 p2tog psso. Must be on a purl row, on a knit row it’d be sk2p.

Thank you so much!!! I’ll try it, hope it works out! Appreciate it so much!!!