Faces = polygons = squares where you "build with"
Edge flow is the flow of the lines, they all have to connect smoothly in order to make a decent model, there are exception for this.
http://www.zbrushcentral.com/attachm...chmentid=68830
As you can see here, all edges connect smoothly with eachother.
http://virtualanvil.files.wordpress....2/goodtris.jpg
As you can see here, the flow gets interrupted which is bad. Try to always use this in most models with exception of flat ones. This causes more faces/polygons but you can always remove lines if the model is completely finished.