The GPS fix quality is measured from the signal source and has more than one possible statuses. All the possible statuses can be seen with the discrete display widget:
Not fixed -> GNSS can't determinate the position ( no signal)
Standalone -> Position is gathered only form GNSS satellites
DGPS -> Differential GPS -> beside GNSS satellites an additional correction from base station is used. Sometimes this status is shown if the received uses additional SBAS signal for the position
RTK fixed -> RTK z with the highest accuracy within the 1-2cm range
RTK float -> if we can not accomplish the RTK fixed state because of the conditions or calculation. The RTK float accuracy is in the range of 0.2-0.5m.