The Steem blockchain has two units of account - STEEM and VESTS. Users who commit their STEEM to a thirteen-week vesting schedule, are provided special benefits within the platform. When STEEM is "powered up", it is converted to VESTS. The ratio "steem_per_mvest" can be found on steemd, it is calculated by taking
total_vesting_fund_steem / (total_vesting_shares / 1,000,000).
VESTS holders are paid 15% of the yearly inflation. The amount of new tokens they receive is directly proportional to the amount of VESTS they hold relative to the total amount of VESTS across all users.
Steem Power does not exist on the blockchain, however, it is what is displayed on the UI in order to keep users from being confused.