This category lists English nouns whose plural is formed irregularly with respect to spelling. For the sake of this category, a noun has a regular plural if it:

• is a symbol or letter and forms its plural by adding -s or -’s
• is a common noun ending in a consonant + y and forms its plural by replacing the -y with -ies
• ends in a sibilant (one of [s], [ʃ], [z], [ʒ]) and has plural ending -es
• does not fall under any of the three cases above and forms its plural by adding -s

Thus this category consists of nouns that don't satisfy any of the above.

For the plural forms themselves see Category:English irregular plurals.