What does PYS stand for?

Pack Your Stuff (CAL)

Parietal Yolk Sac - Cells (DB)

Partial Yield Spectroscopy (MCD)

Photoelectron Yield Spectroscopy

Photo-emission Yield Spectroscopy (SAUS)

Photo Yield Spectroscopy (AAEL)

Primitive Yolk Sac - Embryology