Each conventional aircraft, just because they have wings, they create wake turbulences at wing tips. Since we have high pressure underneath the wing and low pressure above it, this pressure difference converge at the wing tips. Air from high pressure goes up to low pressure zones, plus the forward movement of the airplane create an espiral-like movement of rough air behind the airplane. These wake turbulences are increased (abruptness and size) when dealing with heavy airplanes and low speeds, like the approach stage.

Wake turbulence created by the airplane (NASA)

This rough air does not concern this aircraft, but the aircraft behind it does. Actually, the aircraft behind might fly through this turbulence. As the air is in rotation, it does not keep sticked to the wing foil, so it may cause a lift loss. That’s why ICAO establishes a minimum separation between aircrafts, enroute as well as in approach, in order to avoid rough air. These turbulences drive away because of air viscosity and because of the wind. Even that, they could be 5 miles long and go down up to 900 ft.

In order to decrease these effects, there is a very used and useful tool called winglet, set up at the wing tip, and it slows down the air flow reducing then, the wake turbulence (and the fuel consumption).

Winglet                        Source: Air Guide Online