face_cascade.detectMultiScale(frame, 1.1, 5)

This code is using OpenCV's "Cascade Classifier" to detect faces in a video frame. The "detectMultiScale()" method is used to detect multiple objects (in this case, faces) at different scales within the frame.

The first argument is the video frame that is being analyzed. The second argument, "1.1", is the scale factor. This parameter determines how much the image size is reduced at each image scale. A smaller scale factor will increase the detection time but will improve accuracy. The third argument, "5", is the minimum number of neighboring rectangles that must be detected for a region to be considered a face. The detection process will discard any region that contains fewer rectangles than this value.