In many video files, a meta information called Has B Frames can be found. This has to do with the video compression and compression of the frames of a video. Different frame types can be used as the algorithm for this compression. One of them handles so-called b-frames. Thus, the meta information of Has B Frames tells us, if this particular video algorithm was used.
B-frame refers to a bidirectionally coded picture. It uses image data from both the previous and following frames. Since all these information is used, the b-frame algorithm typically offers a better compression rate.