Ez az úszósáv.

They are doing different jobs here.

• Ez = this
• az = the (the form of the definite article used before a vowel)

So Ez az úszósáv. means literally something like:

• This the swimming-lane.

In natural English, that becomes:

• This is the swimming lane.

A learner often notices that az can also mean that, but here it is not the demonstrative that. Here it is just the definite article the.

Hungarian often omits the verb “to be” in the present tense, third person singular.

So where English says:

• This is the swimming lane.

Hungarian says:

• Ez az úszósáv.

No van is needed here.

This happens in simple identification/equational sentences like:

• Ez egy könyv. = This is a book.
• Az a ház. = That is the house.

But in other contexts, van can appear, so this is a specific grammar pattern, not a general rule that Hungarian never uses is.

Hungarian has two forms of the definite article:

• a before a consonant sound
• az before a vowel sound

Since úszósáv begins with ú, a vowel, the correct article is:

• az úszósáv

Compare:

• a könyv = the book
• az autó = the car

So az is used purely because of the sound that follows.

Úszósáv is a compound noun:

• úszó = swimming / swimmer / swimming-related
• sáv = lane, strip, band

Together, úszósáv means swimming lane.

In context, it usually refers to a lane in a swimming pool.

Hungarian forms many compound nouns like this, so this is a useful pattern to notice.

In this exact form, it is normally understood as a full sentence:

• This is the swimming lane.

That is because Hungarian can leave out is in this kind of sentence.

However, the sequence ez az úszósáv can also appear inside a longer sentence as a noun phrase meaning:

• this swimming lane

For example:

• Ez az úszósáv nagyon keskeny.
• This swimming lane is very narrow.

So the structure can function in more than one way, and context tells you which one is meant.

A rough guide for an English speaker:

• Ez ≈ ez
• az ≈ oz or az, with a short a
• úszósáv ≈ oo-soh-shaav

A few useful pronunciation notes:

• sz is pronounced like English s
• s by itself is pronounced like English sh
• ú, ó, á are long vowels
• Stress in Hungarian is normally on the first syllable of the word:
  • Úszósáv

So:

• úszó has sz = s
• sáv has s = sh

That is why úszósáv sounds roughly like oo-soh-shaav, not oo-zoh-sav.

Because Hungarian does not use a before a vowel. It changes to az.

So:

• a könyv = correct
• az úszósáv = correct
• a úszósáv = incorrect

This is similar to how English changes a to an before a vowel sound.

It is in the nominative form, which is the basic dictionary form of the noun.

There is no special case ending here. The sentence is just identifying something:

• Ez = this
• az úszósáv = the swimming lane

So you are seeing the noun in its plain, uninflected form.

No, that would sound wrong in standard Hungarian.

If you use a demonstrative with a noun, Hungarian normally also keeps the article:

• ez a könyv = this book
• ez az autó = this car
• ez az úszósáv = this swimming lane

So the article is not optional here.

Not always.

• ez commonly means this
• az can mean that
• but a / az can also be the definite article the

So az has two possible roles:

1. demonstrative pronoun: that
2. definite article: the

In Ez az úszósáv., the first word Ez is the demonstrative this, and the second word az is the article the.

That overlap is very common in Hungarian, so it is something learners get used to quickly.