This tool shows current delegation information, filtered as shown in the title. MV stands for a Million Vests. 1MV is approximately equal to 500SP.
It plots the data as a directional network graph where the arrow sizes represent the approximate delegation amount, and the icon sizes show the Hive Power each account owns.
Clicking an account icon highlights the delegation to and from that account.
Clicking an account icon whilst holding down the Shift key opens that account on Hive.