What is a transit visa?
Answer:
If you are a Yemeni for example going on a business trip to Austria, you may have to fly into the UK landing at Gatwick and then transferring to Heathrow to fly on to Austria, your transit visa allows you to travel from Gatwick to Heathrow ie in transit. It would not allow you to stay in the UK.
I would hazard a guess that it might be something to do with changing planes at an airport, to enable you to walk from arrivals to departure boarding gate on the soil of whichever Country you are in. Only a guess but I hope it helps.
The immigration information post by website user , MyTend.com not guarantee correctness