What is this minecraft pocket edition option?

I have Minecraft pocket edition 0.8.1, now I already know what external servers are, but in the options there's an option to tick or untick it says "local server multiplayer" what does this mean? And also another small question if anyone can answer this, what are realms and how come I don't have the option to do it when other mcpe apps seems to have it right there under the "play" button.

It means you can make a server on your Wi-Fi network and people connected to it can play with you. And for the realms it may be because its under maintenance