title: what is f1-score and what its value indicates?
body: <p>There is an evaluation metric on sklearn, it is f1-score(Also f-beta score exists).</p>
  
  <p>I know how to use it, but I could not quite understand what is stands for. </p>
  
  <p>What does it indicates when it is big or small. </p>
  
  <p>if we put formula aside, what should I understand from a f-score value?</p>