STEEM Power (abbreviated SP) is a measurement of how much influence a user has in the Steem network. The more STEEM Power a user holds, the more they can influence the value of posts and comments.
https://steemit.com/faq.html#What_is_the_difference_between_STEEM__STEEM_Power__and_Steem_Dollars
Thank you penguinpablo it's now crystal clear. Good to know that maybe my little votes can influence now and again. I only hope that Steemit grows and remains a good thing. JV