What does the parameter "subsample" mean?

#1

Hi,

What does the parameter “subsample” mean? What is the use of this parameter?

#2

From the docs:

subsample [default=1]
Subsample ratio of the training instances. Setting it to 0.5 means that XGBoost would randomly sample half of the training data prior to growing trees. and this will prevent overfitting. Subsampling will occur once in every boosting iteration.

range: (0,1]