What does UDF mean as a label for my HDD?

[JustStarting]

Accidentally loaded some programs to my Raid 0 setup when I meant to load them onto my backup HDD. I was booted on my backup hdd and forgot windows sees that as drive C when booted up in this configuration. Loaded some programs to drive D- what i thought was my backup drive. When I was done my Raid 0 HDD shows a different icon on my computer. It is a magnifying glass with the letters UDF on it. Does not seem to affect anything, but what does this mean? The icon is the same when I booted under my Raid setup also.

 

[bacillus]

this may help with your UDF understanding!