At the Metaverse Genesis there was only Entropy. It has since been increasing block by block and it makes up the fabric that forms everything in the Metaverse. It is needed for the creation of Assets and Avatars as well as for all other interactions that happen within the Metaverse.
Most Avatars simply refer to Entropy as ETP. It is a scarce resource and there are hordes of miners dedicating their hardware to the search for new Entropy. In order to protect the Metaverse an elite group of Master Nodes has formed to compete for the votes of the Entropy holding Avatars.