Is this term an irregular noun wherein the singular form is also the plural form, or the plural form follows some odd rule?

A noun is considered irregular when

  1. it is an uncountable mass noun
  2. the term or phrase ends in a plural
  3. the noun does not follow any of the regular noun pluralization rules

Noun pluralization rules

nouns that end in...

  1. Most nouns add s to the end.
    cat – cats;
    car – cars;
    team – teams
  2. ch, sh, s, x, or z  where es  is added to the end
    church – churches;
    tax ­­­­– taxes;
    pass – passes 
  3. or fe   where the f or fe becomes ves where  s is added to the end
    elf – elves; 
    loaf – loaves; 
    thief – thieves
  4. vowel and y where s is added to the end
    toy – toys;
    boy – boys;
    employ – employs
  5. vowel and o add s to the end
    video – videos;
    studio – studios;
    zoo – zoos
  6. consonant and y where y becomes ies
    baby – babies;
    country – countries;
    spy – spies
  7. consonant and o where es is added to the end
    hero – heroes;
    potato – potatoes;
    volcano – volcanoes