What is the use of transition map and what is "seamless transition" in UE4?

Since there is no much information about it, I thought to post it here and learn more about it. After some research I have found that it’s being used in a system called “seamless transition” which is used to load maps seamlessly. Also there is a system called level streaming which helps you load the game map sub level by sub level. I have already used level streaming in my projects. Is this “seamless transition” behave just like level streaming? or its a completely different thing?

Can “seamless transition” used in single player games or is it only for multiplayer games? Please help me to clarify these information.

Thank you.