An umbrella term for the geomorphological processes that lower the surface of a landscape by means other than water erosion. As you might expect, deflation has its greatest effect in desert landscapes.
The most common cause of deflation is wind, as it picks up fine particles from a dessicated surface. A dried-out lake bed is a common start, or a dried out river channel. First the clay blows away, then the silt, then, when the wind is stronger, the sand. Sometimes the wind is strong enough to pick up small pebbles, at least enough to make them bounce along the surface (saltation). Deflation, then, is an effect of particle sorting by the wind.
The fine particles blow away and form loess and sand dunes elsewhere, leaving behind the stones that are too big for the wind to pick up. These stones jostle against each other as the soil beneath them is carried away, only stopping when they fit together well enough to protect the soil from the wind. Eventually an equilibrium surface is reached. Such a self-assembled jigsaw puzzle of stone is called a desert pavement by geomorphologists; it is called Gobi in Mongolian, reg in Arabic, and gibber in Australia. Whatever you call it, it's the most common form of desert surface.
The process begins again when the the wind concentrates on a particular spot, or finds a weak spot or a hole in the pavement. Perhaps a watering hole is wallowed out by buffalo or elephants, or someone thoughtlessly drives a jeep across the pavement, or simply walks across it in hard boots. A little bit of soil exposed and is carried away by the wind. This renewed deflation is self-reinforcing: more and more rocks are jostled from their equilibrium state, more and more soil is exposed and carried away.
Such a "deflation hollow" can be carved down until it reaches the water table (forming a playa lake at the bottom); it spreads out until a new equilibrium surface forms. When the water table is particularly deep, enormous deflation hollows or "pan"s can form. One of the largest, Egypt's Qattara Depression, is 18,000 km2 in extent, and 122m below sea level.
Although deflation originates from natural processes, man can help it along: Dried-out or poorly managed farmland is just as likely a source. East Anglia's strong "fen blows" are well known for carrying top soil away. A more dramatic (tragic) example is the Dust Bowl of the 1930's in the United States.