What do you understand by regular and irregular noun?

A regular plural is a noun to which an -s or an -es is added to form the plural.

An irregular plural noun is Word that forms the plurals in some other way.

Examples of irregular plural nouns:

singular / plural

mouse / mice

man / men

woman / women

child / children

person / people

goose / geese

ox / oxen

foot / feet

tooth / teeth

cactus / cacti

alumnus / alumni

medium / media