oneureun beoseuga neujeoyo.

은 is the topic particle. In 오늘은, it marks today as the topic: as for today / today in particular.

So the sentence has a slight nuance of contrast, like:

• Today, the bus is late.
• At least today, the bus is late.

This does not always mean a strong contrast, but it often gives that feeling of setting the scene: speaking of today...

Without 은, 오늘 버스가 늦어요 is also possible, but 오늘은 sounds a bit more natural when you are talking about today's situation specifically.

Because 버스 is the subject here, not the object.

• 가/이 = subject marker
• 를/을 = object marker

In this sentence, the bus is the thing that is late, so it takes 가:

• 버스가 늦어요 = The bus is late

If you used 버스를, it would sound like the bus is the object of some action, which does not fit with 늦어요 here.

The dictionary form is 늦다.

In this sentence, 늦어요 is the polite present-style form of 늦다.

You can think of it like this:

• dictionary form: 늦다
• polite form: 늦어요

It means to be late or to run late, depending on context.

In Korean grammar, 늦다 is usually treated as a descriptive verb (often called an adjective in learner-friendly explanations).

That means it behaves differently from English adjectives. In English, you say:

• The bus is late

In Korean, the word for late acts more like a predicate by itself:

• 버스가 늦어요

So Korean does not need a separate word like is in this sentence.

It can naturally cover both ideas depending on context.

With a bus, 버스가 늦어요 usually means:

• The bus is late
• The bus is running late
• The bus is coming late

Korean often leaves this a little broader than English. The exact nuance comes from the situation.

Korean often uses the present form for a current situation or an ongoing state.

So 오늘은 버스가 늦어요 means that today, the bus is late as a present state. It does not need a special progressive form like English sometimes does with is running late.

The present polite form 늦어요 is the normal way to say this.

Both are possible, but there is a nuance difference.

• 오늘은 버스가 늦어요: As for today, the bus is late.
  This highlights today as the topic and can imply contrast.

• 오늘 버스가 늦어요: The bus is late today.
  This is a bit more neutral and simply adds today as time information.

So 은 adds topic/contrast flavor, while leaving it out makes the sentence more plain.

Yes, but the nuance changes.

• 버스가 늦어요 focuses on the bus as the subject of the statement.
• 버스는 늦어요 makes the bus the topic, often with a contrastive feeling, like:
  • As for the bus, it’s late.
  • maybe implying but something else is not

In your sentence, 오늘은 버스가 늦어요 is very natural because:

• 오늘은 sets the topic
• 버스가 identifies what is late today

Using both this way is common in Korean.

늦어요 is in the polite informal style, also called 해요체. It is very common in everyday conversation.

Compare:

• 늦어 = casual
• 늦어요 = polite everyday speech
• 늦습니다 = formal polite

So:

• 오늘은 버스가 늦어요 is natural and polite for normal conversation.
• 오늘은 버스가 늦습니다 would sound more formal, like an announcement or formal report.

Korean word order is more flexible than English, but some orders sound more natural than others.

The most neutral order here is:

• 오늘은 버스가 늦어요

You may also hear:

• 버스가 오늘은 늦어요

This can sound more marked, with extra emphasis on today.

Because Korean uses particles like 은 and 가, the roles of the words stay clear even if the order changes. Still, for learners, it is best to use the basic, natural order first.

Korean usually does not use articles like the or a.

So 버스가 늦어요 could mean:

• the bus is late
• a bus is late
• my/usual/the expected bus is late

The exact meaning comes from context. In real conversation, both speaker and listener usually already know which bus is being talked about.

That is very normal in Korean. Context does a lot of the work that articles do in English.