The category of number

English count nouns have singular and plural forms. These nouns are called variable nouns. Singular nouns denotes one, plural ― more than one. Other nouns are used either only in the singular or only in the plural. They are called invariable nouns.
Variable nouns (regular plurals): Noun + -s/-es. The suffix -es is added to nouns ending in:-s, ss, sh, ch, x, z, o: glasses, watches, tomatoes, heroes.

Nouns in -o have the plural in -os: a) after a vowel: zoos, radios; b) in proper names: Romeos, Eskimos; c) in abbreviations: photos, kilos; d) in musical terms of Italian origin: pianos, solos, tangos, sopranos.

Nouns ending in -y, preceded by a consonant, change -y into -ies: stories, flies. Only -s is added: a) after a vowel: boys, toys; b) in proper names: the Kennedys, Marys; c) to compounds: stand-bys, lay-bys.

Note: The plural of abbreviations is sometimes formed in spelling by doubling a letter: Ms (manuscript) ― MSS, p. (page) ― pp., Mr (Mister) ― Messers, MP (Member of Parliament) ― MPs ['em'pi:z] (or MP's), MD (Doctor of Medicine) ― MDs ['em'di:z].
Irregular plurals. They form their plural by:

1) a change of a vowel: man ― men, woman ― women, tooth - teeth, foot ― feet, mouse ― mice, goose ― geese, louse ― lice;
2) voicing (twelve nouns ending in -f (e) form their plural changing -f(e) into-ve: wives, lives, wolves, calves, knives, halves, selves, shelves, thieves, leaves, elves, loaves. In other cases -fs: proofs, beliefs, still-lifes, etc. In a few cases both -fs and -ves forms are possible: scarf ― scarfs (-ves), dwarf ― dwarfs (-ves), handkerchief ― handkerchiefs(-ves);
3) -en plural: ox ― oxen, child ― children, brother― brethren;
4) retaining the singular form in the plural: a) a sheep ― sheep, a swine ― swine, a deer ― deer, a fish ― fish, a craft ― craft, b) nationality nouns in -ese, -ss: Japanese ― the Japanese, a Swiss ― the Swiss; с) quantitative nouns: hundred, thousand, million, dozen, stone (3 dozen eggs, but dozens of people);
5) retaining -s of the singular unchained in the plural: a means ― means, a works  ― works, a barracks ― barracks, a headquarters ― headquarters, a series ― series, a species ― species;
6) plurals of foreign origin: -us — -i [ai]: stimulus – stimuli; -a — -ae [i:]: vertebra ― vertebrae, formula ― formulae; -um — -a [a:]: datum – data; -is [iz] — -es [iz]: basis – bases, crisis ― crises; -on — -a [a:]: phenomenon – phenomena, -ex, -ix — -ices: appendix – appendices.

The noun - semantic characteristics

Nouns are names of objects, i.e. things, human beings, animals, materials, abstract notions, states (e.g. table, house, man, dog, snow, music, love, sleep).

Semantic characteristics.

All nouns can be divided into two main groups: proper nouns and common nouns.

A proper noun is used for a particular person, place, thing or idea that is unique. It is generally spelled with a capital letter. Sometimes proper names can be used as common nouns: Ford ― a Ford = a car; Repin ― a Repin = a painter like Repin, etc.)

Common nouns can be classified into count nouns (denoting object that can becounted), uncount nouns (denoting object that cannot be counted) and collective nouns (denoting a group of persons)

Count nouns may be concrete denoting animate (boy, child) or inanimate (table, book, tree) objects and abstract (idea, question, problem).

Uncount nouns nouns may be abstract (fun, socialism) or material (bread,iron).

Many uncount nouns can also beсome countable in certain contexts.(He bought an evening paper.- He bought wallpaper.)

Collective nouns may be nouns of multitude (people, police, etc.) or collective proper (family, company, staff etc.) Collective nouns of multitude are used in the plural. Collective nouns proper are used in two ways: if you regard a particular noun as a single body, it is used in the singular: The audience was enormous. If you regard a noun as a group or persons, then it is used in the plural: My family are watching TV now.

More about nouns could be found here: http://uastudent.com/noun-morphemic-structure/