Exposure with respect to site selection for growing garden or larger scale crops refers to both light and situation. Exposure is concerned with how much light a garden or field receives and the way in which the light hits it. It is also concerned with the directional orientation of a site, the way that it faces, affecting the way in which the light, winds and rains hit it.
The same garden or field can have different exposures, which in turn can create microclimates. A gardener or farmer may find a plant does really well in one area but poorly in another, due in part to the varied exposures.
Northern or southern exposures can have either warming or cooling effects, depending on which hemisphere you're situated in. Knowing the way that the predominant winds blow, the amount of sunshine and any quirks that might impact the garden or field can help you to plan the optimal placement of food and other crops and garden plants.