La reunión es a las ocho.

Because ser is used to identify or define something, and here the sentence is stating a scheduled time for the meeting.

• La reunión es a las ocho = the meeting is at eight / the meeting takes place at eight.
• Estar is more for location, condition, or temporary state.

So:

• La reunión es a las ocho = correct
• La reunión está a las ocho = not correct in this context

A useful way to think of it is that Spanish often uses ser when talking about an event’s scheduled time:

• La clase es a las nueve
• El concierto es a las diez

Spanish often uses the definite article more than English does.

• La reunión literally means the meeting

In many everyday sentences, Spanish prefers the article where English may or may not use one depending on context. If you are talking about a specific meeting already known in the conversation, la reunión is natural.

If you said just Reunión es a las ocho, it would sound incomplete or unnatural.

Yes, reunión is a feminine noun, and it means meeting.

That is why it takes:

• la reunión for the meeting

Even though many nouns ending in -ión are feminine, it is still something learners usually just memorize with the article:

• la reunión
• la canción
• la información

In Spanish, the normal way to say at a time is a + article + hour.

So:

• a las ocho = at eight
• a las tres = at three
• a las diez = at ten

The a corresponds to at in English.

This is the standard pattern for clock times in Spanish.

Because Spanish time expressions are based on the idea of the hours.

So las ocho literally connects to the eight o’clock hour. That is why Spanish uses the feminine plural article las with most times.

Examples:

• a las dos
• a las cinco
• a las ocho

The exception is one o’clock, because that uses the singular:

• a la una

Because una is singular, while other clock times use the plural pattern.

So:

• a la una = at one
• a las dos = at two
• a las ocho = at eight

This is one of the first special cases learners usually notice. Just remember:

• one o’clock → singular → a la una
• all other hours → plural → a las...

No. You need a before the time.

So:

• La reunión es a las ocho = correct
• La reunión es ocho = incorrect

Spanish needs the time expression introduced properly. The phrase a las ocho works as a unit meaning at eight.

Son las ocho means It’s eight o’clock.

That sentence simply tells the current time.

But La reunión es a las ocho means The meeting is at eight. It tells you when the meeting happens.

So the difference is:

• Son las ocho = the time now is eight
• La reunión es a las ocho = the meeting is scheduled for eight

Both involve time, but they do different jobs.

Reunión is pronounced roughly like reh-oo-nee-ON.

The written accent on -ón shows that the stress falls on the last syllable:

• reu-ni-ÓN

Without the accent mark, Spanish spelling rules would suggest a different stress pattern, so the accent is necessary.

Also, learners often notice the eu in reu-. In normal speech, it flows together smoothly rather than being pronounced as two strongly separated syllables.

Yes, if you want to make the time clearer.

For example:

• La reunión es a las ocho de la mañana = the meeting is at eight in the morning
• La reunión es a las ocho de la tarde = the meeting is at eight in the evening/afternoon

If the context already makes it obvious whether it is morning or evening, Spanish often leaves that part out:

• La reunión es a las ocho

Yes. In everyday writing, schedules, messages, and notices, using the numeral is very common:

• La reunión es a las 8.

Writing it out as ocho is also correct, especially in more careful prose or learning materials.

So both are fine; the difference is mainly style rather than grammar.