Being more specific on meanings: 

-INJ: injects a morph/shape.

-REM: removes a morph/shape.

-MAT: applies a material. 

For older Poser products, all of those were in the Pose section of your library, but the material section came later, I think in Poser 5? Some vendors still create material poses, but for store purposes they require materials to be in the material section nowadays :)

- - - - - - 

Feel free to call me Ohki!

Poser Pro 11, Poser 12 and Poser 13, Windows 10, Superfly junkie. My units are milimeters.

Persephone (the computer): AMD Ryzen 9 5900x, RTX 3070 GPU, 96gb ram.