Variable pools are functional groupings of variables within Service Manager. There are currently four variable pools
A global variable is visible to the entire system. It begins with $G. or $lo..
A local variable is only visible to the RAD application in which it was defined. It begins with $L..
A parameter variable is defined on a parameter command panel. It may contain a value passed in from another application. By convention, parameter variables are written in uppercase letters, such as $PHASE or $GROUP.LIST. Parameter variables are invisible to the debugger.
A thread variable is only visible to the thread in which it was defined. The same variable in different threads has different values, even when the threads are spawned by the same parent.