English words have been traditionally classified into eight parts of speech [also word classes or lexical categories] noun, verb, adjective, pronoun, adverb, preposition, conjunction and interjection.
Noun: a part of speech inflected for case, signifying a concrete or abstract entity such as a person, place, thing or idea.
Verb: any action, occurrence, or process.
Adjective: any qualifier of a noun.
Adverb: any qualifier of an adjective, verb, clause, sentence, or other adverb.
Pronoun: any substitute for a noun or noun phrase.
Preposition: any establisher of relation and syntactic context.
Interjection: any word used to express an emotion or sentiment.
Conjunction: any syntactic connector (F-A-N-B-O-Y-S).
The four main parts of speech in English, namely nouns, verbs, adjectives and adverbs.