This is a version of the 20 newsgroups dataset that is provided in Scikit-learn. From the Scikit-learn docs:
The 20 newsgroups dataset comprises around 18000 newsgroups posts on 20 topics split in two subsets: one for training (or development) and the other one for testing (or for performance evaluation). The split between the train and test set is based upon a messages posted before and after a specific date.
We followed the recommended practice to remove headers, signature blocks, and quotations from each news article.