The online encyclopedia called Wikipedia defines precision farming this way.

Precision farming or precision agriculture is an agricultural concept relying on the existence of in-field variability. It’s about doing the right thing, in the right place, in the right way, at the right time. It requires the use of new technologies, such as global positioning (GPS), sensors, satellites or aerial images, and information management tools (GIS) to assess and understand variations. Collected information may be used to more precisely evaluate optimum sowing density, estimate fertilizers and other inputs needs, and to more accurately predict crop yields. It seeks to avoid applying inflexible practices to a crop, regardless of local soil/climate conditions, and may help to better assess local situations of disease or lodging.

Wikipedia is an open source kind of information resource which lets you edit entries. See if you have something to add.