Мы встретились у казино.

Because встретились means met each other or simply met in the sense of two or more people coming together.

• встретили = met something/someone as a direct object
  
  • for example: Мы встретили Анну = We met Anna
• встретились = met each other / got together / ran into one another

The -сь / -ся ending makes the verb reflexive, and with this verb it often gives a reciprocal meaning: the people involved met one another.

So:

• Мы встретили... = we met someone
• Мы встретились... = we met each other

In this sentence, -сь is the short form of -ся, the reflexive ending.

Russian uses -ся / -сь for several related meanings, including:

• reflexive: doing something to oneself
• reciprocal: doing something to each other
• sometimes a more general intransitive meaning

Here it is mainly reciprocal:

• Мы встретились = We met each other

Why -сь and not -ся?
Because after a vowel, Russian often uses -сь:

• встретили + сь → встретились

Both -ся and -сь are reflexive endings, but the choice depends mostly on sound and form.

In Russian past tense, verbs usually show gender/number, not person.

The base past form here is from встретиться. In the past tense you get:

• встретился = he met
• встретилась = she met
• встретилось = it met
• встретились = they met

So the ending -ли tells you it is plural past.

Because the subject is мы (we), the verb must be plural:

• Мы встретились = We met

Yes, Russian could absolutely say Встретились у казино if the subject is already clear from context.

Russian often omits subject pronouns when they are not needed. The verb form already tells you the action is plural past, and context may make it obvious who we are.

So both are possible:

• Мы встретились у казино. = neutral, explicit
• Встретились у казино. = more natural in many contexts if we is already understood

Including мы can add clarity or slight emphasis.

У usually means by, near, at, outside, next to.

So:

• у казино = by the casino / near the casino
• в казино = in the casino

That is an important difference.

Examples:

• Мы встретились у казино. = We met by/outside/near the casino.
• Мы встретились в казино. = We met inside the casino.

English at the casino can sometimes be a little ambiguous, but Russian is often more specific here.

Normally, у requires the genitive case.

For many nouns, that means the form changes:

• у дома = by the house
• у брата = at my brother’s place / by my brother

But казино is one of many borrowed nouns in Russian that are indeclinable, meaning the form stays the same in all cases.

So even though у requires genitive, the word казино does not change:

• nominative: казино
• genitive after у: казино
• still the same form

This is normal for many foreign words ending in -о, especially words like кино, метро, пальто, кафе, though not all borrowed words behave the same way.

The dictionary form is встретиться.

That is the infinitive, and it is a perfective verb.

Related forms:

• встретиться = to meet, to get together, to meet each other
• встретились = met

There is also an imperfective partner:

• встречаться = to meet, to be meeting, to meet regularly

So:

• Мы встретились у казино. = We met by the casino.
  This refers to a completed meeting event.
• Мы встречались у казино каждый вечер. = We used to meet by the casino every evening.
  This describes repeated or habitual meetings.

This is the classic Russian perfective vs. imperfective contrast.

• встретились = perfective
  Focuses on the completed event: the meeting happened.
• встречались = imperfective
  Focuses on process, repetition, or habit.

Compare:

• Мы встретились у казино.
  = We met by the casino.
  One completed meeting.

• Мы встречались у казино каждую неделю.
  = We used to meet by the casino every week.
  Repeated meetings.

A native English speaker often wants to translate both simply as met, but Russian makes the aspect distinction very clearly.

Yes. Russian word order is flexible, and changing it usually changes emphasis, not the basic meaning.

Possible versions:

• Мы встретились у казино.
  Neutral: We met by the casino.

• У казино мы встретились.
  Emphasizes the location: It was by the casino that we met.

• Встретились мы у казино.
  Can sound more contrastive or stylistic depending on context.

For a learner, the original order is the safest and most neutral.

It is pronounced казино́, with the stress on the last syllable.

So:

• ка-зи-но́

This matters because Russian stress is unpredictable and can change from word to word.

Not necessarily.

встретились can mean:

• met up deliberately
• ran into each other by chance
• simply met without specifying whether it was planned

If you want to make it clearly deliberate, context usually does that. For example:

• Мы договорились и встретились у казино.
  = We arranged it and met by the casino.

If it was accidental, Russian might also say:

• Мы случайно встретились у казино.
  = We accidentally met / ran into each other by the casino.

So the basic sentence itself does not force one interpretation.