Prospin and Inspin
Prospin and Inspin name the same motion: the prop rotates the same direction as the handpath. Most poi spinners say Inspin. The Kinetic Alphabet says Prospin.
Prospin
The prop rotates the same direction as the handpath.
Hand pictograph. Right hand pro-spin shift south to east.
Antispin
The prop rotates in the opposite direction of the handpath.
Hand pictograph. Right hand anti-spin shift south to east.
Why Prospin
Pro and anti are opposites, with and against, so the pair sorts every shift the way the motion does: with the handpath or against it.
In and out already name orientations here, like thumb in and thumb out, so Inspin reads like one of them. Pro isn't an orientation. Prospin only says which way the prop spins.