A person of importance: He really thinks he's someone. (noun)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "someone" in a sentence
"And for a moment like that, to have the gift of sharing a piece of my soul with someone I may never see again ~someone I will never forget, well, I wouldn't trade a moment like that for anything in the world."
"The problem with this new Twitter update is if you follow the White House on Twitter and the White House replies to someone directly, e.g. @someone blah blah blah, you won't see it unless you are also following @someone."
"I mean *someone* posted the photos, so they either took it, or got it from someone else right?"