What GNSS means
GNSS stands for Global Navigation Satellite System. It is the umbrella term for satellite-navigation constellations such as GPS, Galileo, GLONASS and BeiDou. A receiver can use signals from one or several constellations to estimate its position outdoors.
GNSS versus GPS versus RTK
GPS is one specific satellite constellation. GNSS is the broader category. RTK is not a separate constellation at all: it is a correction method applied to compatible GNSS measurements. So an RTK mower is still fundamentally using GNSS, but with extra correction data to improve precision.
Why multiple constellations matter
A mower may see more satellites when it can use several constellations and frequency bands. More usable satellite geometry can improve availability around trees or buildings, although the exact result also depends on antenna design, software and signal reflections. A long list of supported constellations is helpful context, but it is not a guarantee of perfect yard coverage.
What GNSS does not solve
GNSS tells a mower where it is globally, but it does not by itself identify a toy, pet, tree root or flower bed. Those tasks require mapping rules or local sensing such as cameras, LiDAR, ultrasonic sensors or bump sensors. That is why many modern mowers combine GNSS with additional perception systems.
Buyer takeaway
If a mower is sold as wire-free because of satellite positioning, check the complete stack: GNSS capability, correction method, local or network RTK requirements, and the fallback sensors used when satellite conditions are poor.