oneureun hoeuiga se gaena isseoseo bappayo.

은 here marks 오늘 as the topic: as for today.

So 오늘은 gives a sense like:

• Today, ...
• As for today, ...

It sets the time frame for the whole sentence. This is very common in Korean when the speaker is talking about what today is like, compared with other days.

If you said 오늘이, that would sound different because 이/가 marks the subject, not the topic.

가 marks 회의 as the subject of 있다 in this sentence.

The structure is basically:

• 회의가 세 개나 있다 = there are as many as three meetings

Then that whole idea becomes the reason for being busy:

• 회의가 세 개나 있어서 바빠요 = I’m busy because there are as many as three meetings

If you changed it to 회의는, the nuance would shift. 회의는 would make meetings the topic or contrastive topic, something like:

• As for meetings, there are three of them...

That is possible in some contexts, but 회의가 is the natural choice here because the sentence is simply stating that meetings exist/are scheduled.

세 is the native Korean number three, and 개 is a very common general counter.

So:

• 세 개 = three items / three things

In this sentence, 회의 세 개 means three meetings.

Even though 개 is a general counter, it is often used for things that can be counted as separate units, including events in everyday speech. So 회의가 세 개 있다 is a natural way to say there are three meetings.

Korean has two number systems:

• Native Korean numbers: 하나, 둘, 셋, 넷...
• Sino-Korean numbers: 일, 이, 삼, 사...

With counters like 개, Korean usually uses the native Korean numbers.

So:

• 세 개 = correct/natural
• 삼 개 = not natural here

Also, notice that 셋 changes to 세 before a counter:

• 셋
• 세 개

This is a normal pattern:

• 하나 → 한
• 둘 → 두
• 셋 → 세
• 넷 → 네

before many counters.

-나 adds emphasis. Here it means something like:

• as many as three
• no fewer than three
• three whole meetings

So 세 개나 does not just state the number. It shows the speaker feels that three is a lot, probably more than expected or more than they want.

Compare:

• 회의가 세 개 있어서 바빠요 = I’m busy because I have three meetings
• 회의가 세 개나 있어서 바빠요 = I’m busy because I have as many as three meetings

So -나 adds a feeling of surprise, burden, or emphasis.

있어서 comes from 있다 + -아서/어서.

Here, 있다 means to exist / to have. In context:

• 회의가 있다 = there is a meeting / I have a meeting

When changed to 있어서, it connects to the next clause and gives a reason:

• 회의가 세 개나 있어서 = because there are as many as three meetings

So the full sentence is:

• 오늘은 회의가 세 개나 있어서 바빠요
• Today, I’m busy because I have as many as three meetings

That is a very normal Korean sentence pattern.

Korean often puts the background or reason first, and the main statement last:

• 회의가 세 개나 있어서 = because there are as many as three meetings
• 바빠요 = (I’m) busy

So the sentence literally follows a pattern like:

• Today, because there are as many as three meetings, (I’m) busy

This may feel backward compared with English, but it is completely natural in Korean.

Korean often leaves out subjects like I, you, or we when they are obvious from context.

In this sentence, 바빠요 means (I am) busy or sometimes (someone is) busy, depending on context. Since people usually talk about their own schedule this way, I is understood automatically.

So Korean does not need to say:

• 저는 오늘은 회의가 세 개나 있어서 바빠요

That is grammatical, but often unnecessary. Korean prefers omission when the meaning is clear.

바빠요 is the polite, everyday conversational style.

A few related forms:

• 바빠요 = polite casual/plain polite
• 바쁩니다 = more formal
• 바빠서 = because (I’m) busy

In this sentence, 바빠요 is the main final statement:

• I’m busy

The reason is already expressed earlier by 있어서, so you do not need 바빠서.

If you used 바쁩니다, the meaning would be the same, but the tone would be more formal:

• 오늘은 회의가 세 개나 있어서 바쁩니다

Yes, very often.

Literally, 회의가 있다 means a meeting exists or there is a meeting, but in natural English it often translates as:

• I have a meeting
• There is a meeting
• A meeting is scheduled

So:

• 회의가 세 개 있어요 can mean I have three meetings
• or There are three meetings

The exact English translation depends on context, but the Korean expression itself is very common.

Yes. Depending on context and how strongly you want to show the nuance of -나, natural translations include:

• I’m busy today because I have three meetings.
• I’m busy today because I have as many as three meetings.
• Today I’m busy because I’ve got three whole meetings.
• I’m busy today since there are three meetings scheduled.

All of these can work. The key extra nuance is that -나 suggests three feels like a lot.

Yes. That would still be natural and correct.

The difference is nuance:

• 세 개 있어서 = neutral statement of quantity
• 세 개나 있어서 = emphatic; as many as three

So if you just want to state the fact, remove -나. If you want to sound like three is a lot and that’s why I’m busy, keep -나.

In this sentence, 개 is natural because it counts meetings as separate units.

You may also see other expressions in different situations, but they do not always mean exactly the same thing.

For example:

• 회의가 세 번 있다 = there are meetings three times / I have meetings on three occasions
• 회의가 세 개 있다 = there are three meetings

These are similar, but not always identical in nuance. 세 개 focuses on the number of meetings as countable items; 세 번 focuses more on the number of occurrences.

For a learner, 회의가 세 개 있다 is a very good and natural pattern to know.

You can break it down like this:

• 오늘은 = as for today
• 회의가 = meetings (subject)
• 세 개나 = as many as three
• 있어서 = because there are / because I have
• 바빠요 = I’m busy

So the structure is:

• [topic/time] + [subject] + [number + counter + emphasis] + [reason connector] + [main statement]

That pattern is very useful in Korean:

• 오늘은 일이 많아서 바빠요 = I’m busy today because I have a lot of work
• 내일은 약속이 두 개나 있어서 바빠요 = I’m busy tomorrow because I have as many as two plans

So this sentence is a great example of a very common Korean way of explaining why someone is busy.