Мой друг ждёт у двери.

Мой means my and agrees with the noun it describes. Since друг is masculine singular, the correct form is мой.

Compare:

• мой друг = my friend
• моя подруга = my female friend
• моё окно = my window
• мои друзья = my friends

So мой друг is the natural masculine form.

Друг is in the nominative case because it is the subject of the sentence — the person doing the action.

In Мой друг ждёт у двери, the subject is мой друг = my friend, and the verb is ждёт = is waiting / waits.

Ждать is the dictionary form (the infinitive), meaning to wait.

In the sentence, you need a conjugated verb, because the subject is мой друг = my friend = he.
So ждать changes to ждёт, which is the 3rd person singular present tense form:

• я жду = I wait / am waiting
• ты ждёшь = you wait
• он / она ждёт = he / she waits
• мы ждём = we wait
• вы ждёте = you wait
• они ждут = they wait

So мой друг ждёт literally means my friend waits / is waiting.

The letter ё shows both pronunciation and stress.

• ждёт is pronounced roughly like zhdyot
• The stress falls on ё

In many Russian texts, ё is often written as е, so you may see ждет in informal printing, but it is still pronounced ждёт.

For learners, it is helpful to remember the correct form with ё.

Because the preposition у requires the genitive case.

The noun дверь is the dictionary form, but after у it changes to the genitive singular form:

• дверь = door
• у двери = at/by the door

So the pattern is:

• у дома = by the house
• у окна = by the window
• у двери = by the door

That is why у дверь is incorrect.

Here двери is genitive singular of дверь.

This is one of the forms of дверь:

• nominative: дверь
• genitive: двери
• dative: двери
• accusative: дверь
• instrumental: дверью
• prepositional: двери

So in this sentence, двери is used because у takes the genitive.

It can mean any of those, depending on context. The core idea is position next to / near something.

So у двери can be translated naturally as:

• at the door
• by the door
• near the door

It does not mean that the friend is inside the doorway. It simply places him close to the door.

Russian has no articles, so there is no direct equivalent of a or the.

English says:

• My friend is waiting at the door

Russian simply says:

• Мой друг ждёт у двери

Whether the meaning is a door or the door is understood from context.

Yes, ждать often takes a direct object:

• ждать друга = to wait for a friend
• ждать автобус = to wait for the bus

But it does not have to state the object if it is already known or not important. In this sentence, the focus is on where the friend is waiting, not whom/what he is waiting for.

So:

• Мой друг ждёт у двери = My friend is waiting by the door

The phrase у двери tells us the location, not the thing being waited for.

Ждать is imperfective.

Russian uses the imperfective here because waiting is seen as an ongoing process or state, not a completed action. That matches English is waiting very well.

So ждёт can mean:

• waits
• is waiting

depending on context.

Yes. Russian word order is more flexible than English because case endings show the grammatical roles.

The neutral order here is:

• Мой друг ждёт у двери.

But you could also say:

• У двери ждёт мой друг.
• Ждёт мой друг у двери.

These all keep the basic meaning, but the emphasis changes:

• Мой друг ждёт у двери = neutral
• У двери ждёт мой друг = emphasizes by the door
• Ждёт мой друг у двери = more marked, often stylistic or context-driven

Grammatically, yes, but the meaning changes.

• Мой друг ждёт у двери = My friend is waiting by the door
• Друг ждёт у двери = A friend / the friend is waiting by the door

Without мой, you lose the idea of my. Russian often omits possessive words when context makes them unnecessary, but if you specifically want to say my friend, you keep мой.

Друг usually refers to a male friend, while подруга refers to a female friend.

So:

• мой друг = my male friend
• моя подруга = my female friend

If the friend is female, the whole phrase would change:

• Моя подруга ждёт у двери.

Notice that моя agrees with подруга, which is feminine.