What is the meaning of "Ranked # out of #"? and Level in Ranking?

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I recently visited my profile and noticed a link for ranking of interests, after clicking on this link, I viewed several discussion interests with a level example "Level 8 ranked 12238 out of 23000". Does ranking means that the my lot users click the + or - or ! buttons. How do you define levels in ranking? Please help me out. Ferritic