Definitions

The importance of definitions in reaching an audience is pretty simple.  There are many times an author may use words that their audience has never heard before, and using definitions can get the audience up to speed quickly and without too much straining.  The best example of this is when an author is writing about something specific to them or their job.  They might be using words or slang that only people in their field know.  If they define them then the audience will learn and understand those words.