Could refer to "University," a specific "Unit," or part of a sequenced naming convention (e.g., Unit 8).
Can you provide more on where you found this file or what you expect to see in the video?
Often recommended because it includes its own codecs and can play almost any MP4 file, even if it is slightly corrupted.
If the video has sound but no picture (or vice versa), it may be encoded with a specific codec. Tools like Handbrake can convert it into a more standard MP4 format.