Όλοι περιμένουν στη στάση γιατί το λεωφορείο αργεί.

Here Όλοι means everyone or all of them. It is the masculine plural form, and Greek often uses the masculine plural for a group of people when the group is mixed or unspecified.

So:

• όλοι = all / everyone (masculine or mixed group)
• όλες = all (all-female group)
• όλα = all (things, neuter)

It is acting like a pronoun here, so there is no noun after it.

Greek often drops subject pronouns when they are not needed. The verb ending already tells you who the subject is.

In περιμένουν, the ending -ουν shows that the subject is they.

So:

• περιμένουν = they wait / they are waiting

You could say Αυτοί περιμένουν, but that would add emphasis, like they are the ones waiting.

Περιμένουν is the 3rd person plural, present tense of περιμένω.

That means it can translate as:

• they wait
• they are waiting

Greek present tense often covers both the simple present and the continuous present in English. Context tells you which sounds more natural.

Στη is a contraction of σε + τη(ν).

So:

• σε = in / at / to / on
• τη(ν) = the, feminine accusative singular
• στη = in the / at the / to the

In this sentence, στη στάση means at the stop.

You may also see στην before certain sounds. Here στάση starts with σ, so στη στάση is the normal form.

After σε, Greek normally uses the accusative.

The noun στάση is feminine singular, and in this pattern you get:

• η στάση = the stop, nominative
• τη στάση = the stop, accusative
• στη στάση = at the stop

In this noun, the form στάση itself looks the same in nominative and accusative; the article tells you the case.

Literally, στάση means stop. But in everyday Greek, when the context is transport, η στάση very often means the bus stop.

So in this sentence, στη στάση is naturally understood as at the bus stop.

If needed, Greek can be more explicit:

• στάση λεωφορείου = bus stop

Γιατί can mean both why and because. The context tells you which one it is.

In this sentence, it connects two statements:

• Όλοι περιμένουν στη στάση
• το λεωφορείο αργεί

So here γιατί means because.

Compare:

• Γιατί αργεί το λεωφορείο; = Why is the bus late?
• Όλοι περιμένουν γιατί το λεωφορείο αργεί. = Everyone is waiting because the bus is late.

Greek uses the definite article much more often than English does. In this sentence, το λεωφορείο means the bus—the specific bus people are waiting for, or the bus relevant in the situation.

Leaving the article out would usually sound unnatural here.

So Greek prefers:

• το λεωφορείο αργεί

rather than just:

• λεωφορείο αργεί

It is nominative singular neuter, because it is the subject of αργεί.

Even though το λεωφορείο looks the same in nominative and accusative, its role in the sentence shows that it is nominative:

• το λεωφορείο αργεί = the bus is late

The bus is the thing doing the action or being described, so it is the subject.

Αργεί comes from αργώ. In this sentence it means is late or is delayed.

Depending on context, αργώ can also mean to take a long time.

For example:

• Το λεωφορείο αργεί. = The bus is late.
• Αργεί να έρθει. = It is taking a long time to come.

So the basic idea is lateness or delay.

No, Greek word order is more flexible than English word order. The version you have is a very natural, neutral order:

• Όλοι περιμένουν στη στάση γιατί το λεωφορείο αργεί.

You could also move parts of it for emphasis, for example:

• Στη στάση όλοι περιμένουν γιατί το λεωφορείο αργεί.

That puts a little more focus on στη στάση.

But not every rearrangement sounds equally natural, so flexibility does not mean complete freedom.

Yes. That is very common.

Greek present tense often corresponds to both:

• they wait
• they are waiting

In this sentence, English would usually prefer are waiting, because it describes what is happening right now. But grammatically, Greek just uses the ordinary present tense περιμένουν.