Lipo is a contration for Lithium Polymer batteries.

The simplest explanation would be to say that "LiPo" batteries are a second generation of Lithium Ion Batteries.

For a complete explanation you can check the listing in the Wikipedia Encyclopedia at;

http://en.wikipedia.org/wiki/Lithium-ion_polymer_battery

A "battery bunker" is a reinforced, isolated, fireproof container for your batteries so in case they explode they won't burn down the whole house.