A burst is a column of cool air that, being heavier than warm air, sinks to the ground rapidly and dissipates, causing high winds. When a small portion of such air is laden with water from a storm, and drops to the ground, you get the famous microbursts. (We had one in Chicago about a decade ago, which knocked down nearly every lamppost and tree on my block.) Here’s a particularly vivid one from near Tucson.
A time lapse of a strong thunderstorm that dropped a couple of wet microburst. One in particular was captured really well in the time lapse thanks to the sun peaking out to the west. Notice how the ball of rain falls from the sky and starts separating before hitting the ground. Once it hits the ground you can see the power of microburst as it expands similar to the ripple you would see when you drop a stone in water.
Here’s a figure from Wikipedia that explains what’s happening in the video: that shows what’s happening.
h/t: John W.