Question

what does the word summon mean

Answer 1

A summon in my own understanding means to gather at a hall or assembly for an announcement, speech, etc.

Answer 2

The word 'summon' means to call up. For example, a wizard can use magic to summon a rainstorm, or (more realistically), when you get to be 18, you may get a jury summons from the court, indicating that you need to come be a part of a jury.
Hope that helped! =)