G and GM are the different quality levels of Sony.
At the time of Minolta, the higher quality lenses were labelled with a gold ring. Sony then introduced the GM (G Master), which is positioned above the G class.
https://www.sony.ch/de...

I.e. there are normal lenses, then comes the G class and at the top is the GM class. In the early days of Sony E-mount, lenses were produced in co-operation with ZEISS. They then have the blue Zeiss logo on the lens.

OSS stands for Optical SteadyShot, i.e. the lens has an optical stabiliser.

Hi Tuerler23,

GM : indicates a lens of the Sony Premium G-Master Series
G : This code indicates a G lens
OSS: Indicates optical compensation of camera shake in the lens

The "GM" Series offers more advanced functions than the "G" Series. Sony's proprietary focus drives are constantly evolving in the pursuit of higher drive power and improved dynamic tracking performance. The latest G Master Series is equipped with the XD (extremely dynamic) linear motor, which features superior control technology. This enables better image quality while maintaining the compact form factor.

You can find more detailed information on this topic on our website.

Sony Europe