Remote sensing is the process of acquiring information about objects or areas from a distance.

In broad terms, as you read this sentence, you are performing a type of remote sensing. Your eyes collect visible light waves reflected by the dark and light shapes in front of you, and your brain analyzes this information, assigning letters, words and meanings to the patterns. 

In a geospatial context, remote sensing is defined as the collection of information about the Earth using satellites, aircraft, or drones.