It's the Steem Power delegated to you. With HF 18, there is a new feature where people with huge (or not) Steem Power can delegate (lend) part of their Steem power to one or multiple accounts.
All new user who signs up using Steemit gets delegated some SP by Steemit.inc, as your SP grows, your delegated SP gets pull back when you have enough SP to stand on your own.
Whats HF 18?
Steem Hard Fork 18 .
you can read up abit on here..
https://steemit.com/steem/@ervin-lemark/steem-hard-fork-17-and-hard-fork-18-will-happen-tomorrow-at-15-00-utc
but Hard fork 19 is coming soon.