What is a Good Definition?

             Types of Definitions

sentence  ex. A bookworm is a person who always seems to have his head stuck in a book.

extended  example: We all know what bookworms look like, don’t we? In grade school, they are the kids whom no one wants to play with because they always have their heads between the pages of a book--oblivious to the rest of the world, just like earthworms. Later, in college, they spend their days (and nights) in the library, huddled in their study carrels and glaring at anyone who dares to slow their progress through War and Peace. When they enter the real world, bookworms try to escape into unreality at every chance: they shrink behind their desks and open their books secretively as their office mates gather to pick a fun restaurant for lunch. Bookworms are the dullest of the dull; so says conventional wisdom. In this case, however, conventional wisdom is wrong. Being a bookworm does not mean locking one’s self away for days and ignoring the rest of the world. Rather, it means one is in love with all the adventures and knowledge which the written word holds--all the varieties of life one so rarely encounters in the course of an ordinary day--and one wishes to share these blessings with every innocent passerby. Bookworms are by nature social creatures.
      

--example by Steven Moiles, (with thanks for his permission). 1999. Dept of English Language & Literature, Southern Illinois University Edwardsville

Historical Definition

http://www.oed.com/  The Oxford English Dictionary is a tremendous source for these

Stipulative Definition

Through everyday usage a word can gain a variety of different meanings or shades of meaning (connotations). Many times readers benefit from stipulative definitions, which show precisely how a writer is using a particular term. Stipulative definitions often have an introductory tag phrase, which is boldfaced in the following example:

Example

Since interactivity has become a popular feature, many software developers claim to write "interactive" programs, thus blurring the meaning of the term. For the purposes of this investigation, interactivity results whenever a computer produces output that depends upon a user's input. Most Internet search engines fit this definition since the computer creates a list of "hits" matching the search string supplied by the user. However, submission forms that merely record a user's choices and dump the information in a data file are not truly interactive since the user would receive no substantial output.

This is also an opportunity for the writer to set guidelines for how he/she wishes the stipulated term to be understood.

You may wish to use a term, or coin one, to name a trend or tendency you notice. In this case, you must explain, or stipulate, how you want the reader to understand your use of the term, and thus, the concept.