That 4326 is...
...the ID of the coordinate system used to give the number pairs meaning. This particular ID is published by the European Petroleum Survey Group (ESPG) and is a de-facto standard in the GIS world. 4326 means that the numbers are in Latitude / Longitude, with Greenwich at 0 Lon, and with the WGS84 ellipsoid (a slightly squished sphere) used to model the surface of the earth in order to figure out where those coordinates end up.
Well, now, that should be cleared up.