1.3GB indicates the total size of the video file.
More information on on your computer.
Based on the filename provided, this appears to be a specific digital video file usually found on file-sharing or torrent platforms.
HDmoviesFlix and MoviesFlix refer to the website or "release group" that uploaded or encoded the file.
720p refers to the resolution (High Definition, 1280x720 pixels).
The filename is a standardized naming convention used by online release groups.