ActionScript 3.0

                     pre-loader is essentially a progress bar that shows you the downloading progress of that content.…Without a pre-loader, when you're downloading that external content, the viewer has no idea that that downloading is occurring or…how much longer they have to wait for the download to be complete.…

 

 

Ex:

      Downloading a file from chrome it shows the Progress Bar the to analyze the file is downloaded or not...

            That's the usage of the pre-loader in the actionscript...