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.
