Serial commas refer to the punctuation that separates items in a list; for example:  

                     Oranges, apples, bananas, and grapes are good.

   There will likely be dispute into infinity about whether the last comma (the one before “and grapes") is necessary.

   Legally it could make a huge monetary difference.  For example, if someone’s will and last testament stated, "My entire estate is to be divided between Linda, Sue, Andrew and Rosemary.”  This means that the estate is to be divided only three ways: one full third to Linda, one full third to Sue, and the last third is to be given to Andrew and Rosemary, as one entity, to divide as they see fit.

   However, if it stated, “My entire estate is to be divided between Linda, Sue, Andrew, and Rosemary.” It now means that the estate is divided four ways: one quarter to Linda, one quarter to Sue, one quarter to Andrew, and Rosemary. Linda and Sue both get smaller shares. While Andrew and Rosemary get a specific amount for each of themselves, which may be combined for a total of one half of the estate.

   Thus, if the estate was worth a cool $1M – you can see that in Rosemary's and/or Andrew's case getting a full $150,000 is better than receiving some unknown percentage of 1/3 share and possibly receiving $83,333.33 at best for a payout - as was the case without the last serial comma.

   Academically, if you are working on a paper you should use whichever serial comma style your professor and/or faculty prefers (MLA, APA, or Chicago) for you to use.  Keep in mind these may change from year-to-year. 

Go figure!

Linda Fletcher