title: What does this Code mean? (Train Test Split Scikitlearn)
body: <p>Everywhere I go I see this code. Need help understanding this.</p>
  
  <pre><code>from sklearn.model_selection import train_test_split
  X_train, X_test, y_train, y_test = train_test_split(X,y,testsize = 0.20)
  </code></pre>
  
  <p>what does X_train, X_test, y_train, y_test mean in this context which should I put in fit() and predict()</p>