Regular plural nouns form their plural by adding -s or -es to the singular form (e.g., cat - cats, box - boxes).
Irregular plural nouns don't follow this rule and have their own unique forms. These forms often come from Old English or other languages and are just part of how we use the language today.
Here are some examples:
* Child - Children: This is one of the most common irregular plurals.
* Man - Men: This is another common example.
* Foot - Feet: This is another common example.
* Tooth - Teeth: This is another common example.
* Mouse - Mice: This is another common example.
* Woman - Women: This is another common example.
* Goose - Geese: This is another common example.
It's important to learn these irregular forms as they are commonly used in everyday language.