Local and global variables pass information between locations in your application that you cannot connect with a wire. Use local variables to access front panel objects from more than one location in a single VI. Use global variables to access and pass data among several VIs.
Global variables are built-in LabVIEW objects. When you create a global variable, LabVIEW automatically creates a special global VI, which has a front panel but no block diagram. Add controls and indicators to the front panel of the global VI to define the data types of the global variables it contains. In effect, this front panel is a container from which several VIs can access data.
Local and global variables are advanced LabVIEW concepts. They are inherently not part of the LabVIEW dataflow execution model. Block diagrams can become difficult to read when you use local and global variables, so you should use them carefully.