One way to hold this term: it is a label on a job, not a word you speak. The job is to point at a noun and say, you already know which one. In English only 'the' does that job, so the label sits on 'the' — and it can be lifted off and placed on whichever word does the same job in another language.
One branch
同一張標籤，貼在英文上還是貼在別的語言上
登入就可以看這一支怎麼連回核心畫面。
the word 'the' · noun
The grammar name for the word 'the' in English — the word you put in front of a noun to show that you mean one particular thing that the listener or reader already knows about.
定冠詞（英文的 the）