FDF
From GeoWiki
First Day Finders
A cache that was found within 24hours (approx) from when it was hidden. I guess this is measure of how popular your caches are or how many enthusiastic cachers are in the area.
It is a good thing to see FTF but even better when you see your cache found by so many people.
You can see your First day finds using the GCA menu linked here Your First day finds