Bridge Building!!!!

Can anyone help me understrand what it means to "build a bridge?" I have heard this term thrown around, particularly in the endgame, but would like to discuss some concrete examples.

I invite all to please post examples of bridge building ideas that we may discuss them .  Post them as problems to solve if you like and we can diususs the rationale.

Someone will hopefully post a fuller explanation but if you're impatient you can google, "Lucena position."  This is type of rook and pawn ending (very useful to know... it comes up from time to time) that involves 'building a bridge' ...

and while you're learning rook endings... might as well study the philidor position, too. These two endings are a sort of a yin and yang of rook and pawn endings. 

Great site Pudv. I have one more inquiry.  Why does the rook always come to the 4th rank to build this bridge, and not, pehaps the 5th (which a shorter distance for your king to "walk")? I assume its to keep the distance form the enemy king?

Thanks

I have inserted the information on the website provided by Pudvein, into a board to make it easier to look back through.