[russianbear99]

what is the difference between GP and GS?

[IFly4Him]

Regarding instrument approaches, the glide slope is associated with the VHF frequency that defines the localizer course on an ILS. A glide path gives vertical guidance on a GPS approach but it is derived from a combination of positioning, geometric altitude and ground based signal augmentation. From the pilot's perspective they are applied and flown in a similar fashion.

Regarding visual approaches, the term glide path predates the use of GPS and was a generic term for vertical guidance given by visual cues like a light based system or even the pilot's sense of depth perception.

A good SOP on a nice day is to use a GPS GP as a background reference even if you're technically doing a visual approach.

I have landed on 28 at SFO several times. Given the weather, they were probably doing "Bridge Visuals" but it's still a good idea to have a backup.