Turbulence, in simple terms, is a random flow of air.
We’ll describe several types of this phenomenon.
Mechanical turbulence. When solids – a mountain, a forest, or a house – break the air flow. If the air velocity is low, the flow can simply deflect. But at high speeds, the flow is broken up with the formation of vortices which create a trace - that is already a real turbulence.
If you put your palm against a fast-flowing stream, there will be a slight turbulence right after your palm.
Thermal turbulence. At the ground the air heats up, becomes lighter and begins to rise. At the top there is a cut of the wind - two layers of air are in contact, which have different speeds and directions. Just the boundary between the two layers becomes a zone of turbulence.