https://steemit.com/faq.html#What_is_the_difference_between_STEEM__STEEM_Power__and_Steem_Dollars
This is from the FAQ under the hamburger menu on SteemIt.com.
The short story is SteemPower is what powers your vote. Your posts pay out in a combination of SBD and SteemPower, that steem power is what gives your vote value, the more you hold the larger your vote is.
Great thank you! And thank you for reading and responding to your comments, much appreciated many don’t!