Part of Speech

Part of speech is a class of words (such as adjectives, adverbs, nouns, verbs, etc.) that are defined according to the types of ideas they express and the way they work in a sentence .
A part of speech is also known as a syntactic category or word class. For example, verbs, adjectives, adverbs and prepositions etc. Parts of speech tell us how the word will function in the sentence.
The part of speech is determined by its place in the sentence and by its morphology, not by its meaning.
The notional parts of speech perform certain functions in the sentence. The notional parts of speech:
1. Noun
2. Adjective
3. Pronoun
4. Numeral
5. Verb
6. Adverb
7. Words of the category of state
8. Modal words
9. Interjection
Structural parts of speech express relationships between words/sentences or emphasize the meaning of words/sentences.
They don't have any independent function in the sentence. Structural parts of speech are:
1. Preposition
2. Conjunction
3. Particle
4. Article [3].

Sources:

⠀ 1. Retrieved from: Britannica Online Dictionary [https: //www.britannica. com / dictionary / part of speech]

⠀ 2. Carnie Andrew. (2013). Syntax: A Generative Introduction. USA, New Jersey: Wiley-Blackwell

⠀ 3. Retrieved from: https://www.tspu.edu.ru/tspu/files/fia/files/parts_of_speech.pdf.