Yes, it does stand for 'Friends of Dorothy' a reference to the Wizard of Oz. If a ship is going to have a meeting, it will be in the daily paper. It seems to be a the discretion of the cruise director. I've only, out of 59 cruises, gone to about 3 of them. One was particularly nice as there were a large group of family on board with staff in attendance, another, hosted by a cruise staff member, but a small group and another with no cruise staff in sight.
We finally made it to a FOD party on our last cruise. I ran into one of the assistant CDs and asked if there was going to be one. He said it was already scheduled for the following day and would be listed in the activity sheet.. He turned up to be our host. Only seven of us showed up that afternoon--but it was the same time as a lot of other activities. The assistant CD bought us drinks and basically talked with us a few minutes and then left us to talk amongst ourselves.
On most other cruises, we've run into other gay couples. On one in particular, a couple bought one of the race horses and named it Over the Rainbow. They plastered the ship with signs about their horse--some of the too clever for a lot of folks to get. It was a lot of fun--even though they lost the race.