Article (grammar) - Wikipedia
https://en.wikipedia.org/wiki/Article_(grammar)
An article is any member of a class of dedicated words that are used with noun phrases to mark the identifiability of the referents of the noun phrases. The category of articles constitutes a part of speech.
A, An, The - Articles in English - English Study Page
https://englishstudypage.com/grammar/a-an-the-articles-in-english/
These additions are called "Articles" which is any of the English words "a", "an", and "the". They identify whether a noun is definite (specific or particular) or indefinite (general or unspecific).
How to Use Articles (a/an/the) // Purdue Writing Lab
https://owl.purdue.edu/owl/general_writing/grammar/using_articles.html
Basically, an article is an adjective. Like adjectives, articles modify nouns. English has two articles: the and a/an. We call the the definite article and a/an the indefinite article.
Articles - 'a', 'an' and 'the' | English Grammar - YouTube
https://www.youtube.com/watch?v=zmR_CYJrz8o
Learn when and how to use the articles 'a', 'an' and 'the' in this English grammar lesson. We will end the lesson with a gap-filling exercise...
A/an and the — English Grammar Today — Cambridge Dictionary
https://dictionary.cambridge.org/ru/%D0%B3%D1%80%D0%B0%D0%BC%D0%BC%D0%B0%D1%82%D0%B8%D0%BA%D0%B0/%D0%B1%D1%80%D0%B8%D1%82%D0%B0%D0%BD%D1%81%D0%BA%D0%B0%D1%8F-%D0%B3%D1%80%D0%B0%D0%BC%D0%BC%D0%B0%D1%82%D0%B8%D0%BA%D0%B0/a-an-and-the
A/an before a noun shows that what is referred to is not already known to the speaker, listener, writer and/or reader (it is the indefinite article)