In-joke
In-jokes are comedy elements added to a production or a situation. The comedy comes from shared knowledge between a specific group such as co-workers, members of the same organization or people with a shared belief or knowledge of a shared situation.

There are many in-jokes that people have added to displays and scripts for Star Trek over the last 50 years. 

Examples include:

 the recurrence of the number 47
 various displays on okudagrams and indeed the name okudagram itself
 references in the Star Trek universe to other science fiction shows and movies
 references to real world facts about other Star Trek series (Camus II)
 the "sharing" of planets and species between Star Trek and other science fiction
 nicknames for production staff or crew making it into references within continuity (see: great bird/s of the galaxy) and so on.

See also 
 Popular culture references in Star Trek
 Star Trek parodies and pop culture references

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Star Trek and pop culture
Plot devices