Using runtime shared libraries

You can sometimes improve download time by using runtime shared libraries. These libraries are usually necessary for larger applications or when numerous applications on a site use the same components or symbols. By externalizing the common assets of your SWF files, you do not download classes repeatedly. The first SWF file that uses a shared library has a longer download time, because both the SWF file and the library load. The library caches on the user’s computer, and then all the subsequent SWF files use the library. This process can greatly improve download time for some larger applications.

  This page on the Web