I have done a google search and really can't find a definitive description of what this file is.
The location is on the EFI System Partition in /EFI/APPLE/EXTENSIONS. It's not present either after creating a new GPT and partitioning scheme, nor after installing Mac OS. It appears to be downloaded and installed within a couple of minutes of first boot and login. I haven't zero'd in on the exact moment or what service is doing this. But if there is no network connection, the file does not appear after 1/2 hour.
The file is byte for byte identical on two different models of Macbook Pros (2008 and 2011) with two different EFI firmware versions, with two different versions of Mac OS (10.6.7 and 10.7.0).