One of the things that can be quite confusing when you start working with geospatial data is the notion of a spatial reference system. Imagine that you're running a search-and-rescue operation, and are given the location of a plane crash as a coordinate, for example:
What do these numbers mean? Are these values a latitude and longitude, or are they perhaps a number of kilometers away from a given reference point? Without understanding how these coordinates translate to a point on the Earth's surface, you'd have no way of knowing where to send your rescuers.
Spatial reference systems are sometimes referred to as coordinate reference systems. Don't worry: these two terms refer to the same ...