G38.2 is for probing on an axis. In this case it is probing on the Z axis. The Z axis is slowly lowered until the ‘probe’ (which is system specific) senses contact with the material and, when it does, the motion is stopped. At that point the Z value would be zeroed (or set to some consistent over travel value) and then the torch is moved to a new Z height (typically the pierce height) and cutting can begin. This is usually done before every pierce in case the material is warped or the table isn’t level, etc.
In my experience, G codes for any system are ‘similar’, but I’d never call it a ‘standard’ as the definitions are not guided by any standards authority. De facto standard in some cases, but even there there are variations.