The document discusses Mask R-CNN, an extension of Faster R-CNN object detection that also performs semantic segmentation. Mask R-CNN adds a branch for predicting segmentation masks on each Region of Interest independently of class. During training, the mask branch learns to segment objects regardless of class, and at test time predicts masks for all classes using a "winner takes all" approach. The document also compares Mask R-CNN to Faster R-CNN and FCN approaches.