It is where recording started
A phone writes one position for the whole clip. If someone walked a kilometre while filming, the pin shows the start. Action cameras with a GPS track are the exception: they log the whole route.
Accuracy varies
Outdoors with a clear sky, a phone fix is usually good to a few metres. Indoors, in a city canyon or straight after switching the phone on, it can be tens or hundreds of metres out, or be the last position the phone knew. When the file stores an accuracy value, it is shown next to the coordinates. If an iPhone had Precise Location turned off for Camera, the position is deliberately approximate.
It can be changed
Location is ordinary metadata. Anyone with an editor, including the video metadata editor on this site, can move the pin or add one that was never recorded. A location is good evidence for your own original files and weak evidence for a stranger’s. Check it against the date, the device and what the picture shows, and look at Provenance for signs the file was re-saved. The video forensics guide goes further.