"The apple is food."
(edit*) my apologies, i didnt see all my typos at once.
in korean, the subject marker ( 이/가 ) attaches to the actor noun in the sentence.
Then the topic marker ( 은/는 ) is used for a noun compared or described or for emphasizing its quality.
In English, the topic is the primary idea of the sentence or a paragraph. In English, there is no grammatical marker for a topic word.
*The object noun will have ( 을/를 ) particle.
Also I think the confusion for me as an English speaker comes from several ideas in English.
Subject = Topic or main thought of a sentence, discussion, paragraph, or seminar.
Subject = main actor in a sentence.
Object = the thing being acted on.
Topic particles in Korean have multiple distinctly different uses. English requires so many more words to achieve those different meanings.
As for terminology for each language, I want to see and learn the Korean terms if they are unique to Korean such as its particles.
Likewise from English: The Korean "particles" we have studied so far are added to the end of words are listed as "markers". In English, they are called "suffixes".
Something like, a topic is something you are talking about or going to talk about. They are marked with 은/는. It gives context/background to the conversation. But once you have mentioned the topic, you don't have to keep mentioning it. So you don't have to keep adding 은/는, or mentioning the topic.
"저는 ..." is like "as for me ..." and you would continue talking about yourself, but you don't have to keep saying "I/me".
A subject, I think of as sonething you want to identify. Like who, what, which one etc. "제가 ..." is like "it is none other than me..."
"WHO is the best?" "제가요." (It's me.)
That was my understanding, please correct me if I'm wrong.