Buzzing is the act of flying close to people who are stationary or slow-moving. A wingsuit skydiver for example might buzz a tandem skydiver [left] by flying past at high speed, a hot air balloon or a paraglider. Generally this will have been pre-planned on the ground.
As wingsuits can travel up to 225kph compared to a tandem canopy which can travel at 0kph when facing into wind, the relative passing speed can be very high.
Proximity Flyers (Low Clearance Wingsuit BASE Jumpers) have also been known to buzz people and buildings on the ground.