OpenCV - What type of a result does cv2.goodFeaturesToTrack() return?
The cv2.goodFeaturesToTrack() is mainly used for detection of corners. See THIS PAGE

If you observe the type of the value returned by  cv2.goodFeaturesToTrack(), it is numpy.ndarray, which is a multi-dimensional array according to THIS DOCUMENT

So the function cv2.goodFeaturesToTrack() returns all the locations of the corners present in the gray scale image.

This is what a typical output would look like, the corners are marked in blue: