One of those rare instances that necessitates the use of an Oxford (or serial) comma.
Because WITHOUT the Oxford comma, the parenthetical information is confusing and could be understood to mean that the “enabling media” is approximated1 (“~”) as “fluids,” and by the inclusion of “or,” “fluids” “could also be called” “force-fields.”
Including the Oxford comma disambiguates the parenthetical information by clearly distinguishing “fluids” and “force-fields” as different entities in the approximation.
Generally, however, the serial comma is unnecessary when confusing either/or possibilities of interpretation DO NOT arise without it.
Thus, this exception that requires an Oxford comma does not prove the rule that the Oxford comma should always be used as a stylistic thing.
- “approximated” in this context means “can be thought of as” or “called” etc. Apologies for all the quotes. I had thought of using alternating ” and ‘ sets, but I don’t believe that would be a proper construction. [… mean that the “enabling media” is approximated* (“~”) as ‘fluids,’ and by the inclusion of “or,” ‘fluids’ “could also be called” ‘force-fields.’] I think the “proper” construction is better.