Ok, so I have attempted to look all over the internet and cannot seem to find the meanings of terms said at JFK Tower, and Ground. these include, alpha, bravo, echo, charlie, November etc.. I read somewhere on VATSIM that they represent letters A-Z, but I still don't get what they mean. For example.. JFK ground repeatedly said " Hold short of echo" for about 6 flights straight.. what is all of this? Anywhere I can read about it?