Grid File Access Library
The Grid File Access Library, or gfal, is a library developed by LCG to allow applications to easily access and store files across the grid (OK, you could probably have guessed that from the name...). It's the underlying library providing much of the functionality to LCG Utils.
The RPM to be installed is GFAL-client, and it should be installed by default for nodes which require this functionality, i.e., WNs and UIs.
For application developers GFAL is documented through man pages bundled with the RPM, which are also available here: