What is the 107% rule?

In F1 Racing the 107% rule pertains to qualifying times. It was introduced in 1996 as a safety measure.

What is the 107% rule in F1?
The 107% rule in a Formula 1 is a regulation that requires each driver to set a lap time within 107% of the fastest qualifying time in order to be able to compete in the race. If a driver fails to do so, they will not be allowed to start the race.

https://formulapedia.com/107-percent-rule-f1/

But what does it mean, please? If the pole position drove a 100mph lap, would everyone else have to drive at 107mph just to get in? I can't see how it could possibly be that, so what is it please? How can you have over 100% of anything?

It is not 107% of the speed, but 107% of the time for the fastest lap in qualifying rounds. (The link in the first answer has this explanation.)

Say the fastest time was 100 seconds. Then all the others must finish within 100 x 1.07 = 107 seconds. If they take longer than that, they do not qualify to compete in the race.

In theory this makes the race safer, since it removes non-competitive cars that may get in the way of the faster ones and cause accidents.