What does the value of ‘leaf’ in the following xgboost model tree diagram means?

I am guessing that it is conditional probability given that the above (tree branch) condition exists. However, I am not clear on it.

If you want to read more about the data used or how do we get this diagram then go to : http://machinelearningmastery.com/visualize-gradient-boosting-decision-trees-xgboost-python/

Answer

Attribute leaf is the predicted value. In other words, if the evaluation of a tree model ends at that terminal node (aka leaf node), then this is the value that is returned.

In pseudocode (the left-most branch of your tree model):

if(f1 < 127.5){
  if(f7 < 28.5){
    if(f5 < 45.4){
      return 0.167528f;
    } else {
      return 0.05f;
    }
  }
}