That is the number of vests. The amount of SP equates to vests. It is the weight that your vote is worth. There are two types of voting weight. The first type is for your normal voting. These vests are a combination of the amount of SP you have and the amount of Delegated SP. Then there is the type that is only for witness voting. These vests are only calculated from the amount of SP you own and does not include delegation.

Lets say for instance:

• To be ranked as a whale, one would need 1 Billion Vests.
• To be ranked as an orca, one would need 100 Million Vest
• To be ranked as a dolphin, one would need 10 Million Vests
• To be ranked as a minnow, one would need 1 Million Vests

To put this in perspective, our combined voting power so far is about 1/3 of a Whale Vote. Right now there are only 37 active whales on Steemit.