That means old little uncle Dennis. He may not be little, but still, sometimes it just is a diminuative, though that doesn’t properly describe him either. He is a big man with a lot of hair, that I can say without any thinking. He has long hair and an even longer beard.
Well, to put it in short, we are now at his house after a very long day of driving. I have been counting down the days until coming to Dennis’s house for a long time, since Australia actually. At his house, he has several pets, including a tortoise.
The reason that we call him Oom or Oomitjie (uncle or little uncle) is because here you call respected older people Oom or Tannie (uncle or aunt, respectively).