Ez a biztonsági kód.

In Hungarian, the verb van (to be) is usually left out in the present tense, third person singular when you are saying that one thing is another.

So:

• Ez a biztonsági kód. = This is the security code.

But in past or future, or with other persons, the verb appears:

• Ez volt a biztonsági kód. = This was the security code.
• Ez a biztonsági kód lesz. = This will be the security code.
• Én vagyok a tanár. = I am the teacher.

So the missing is is completely normal here.

Ez means this.

It is the near demonstrative, used for something close to the speaker, either physically or in the conversation.

Compare:

• ez = this
• az = that

So Ez a biztonsági kód. starts with This...

In Hungarian, when a demonstrative like ez (this) comes before a noun, the noun normally still keeps its article.

So Hungarian says:

• ez a kód = this code
• az a kód = that code

This is a very common Hungarian pattern:

• ez a ház = this house
• az a könyv = that book

So ez a biztonsági kód is the normal structure.
Without a, it would sound wrong in standard Hungarian.

Hungarian has two forms of the definite article:

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

Since biztonsági starts with b, a consonant, Hungarian uses a:

• a biztonsági kód

Compare:

• az autó = the car
• az iskola = the school
• a ház = the house

So ez a biztonsági kód is correct because the next word begins with a consonant.

Biztonsági is an adjective meaning something like security-related or safety-related, depending on context.

It comes from the noun:

• biztonság = security / safety

and the suffix:

• -i = a common adjective-forming suffix meaning related to or associated with

So:

• biztonság → biztonsági
• security/safety → security-/safety-related

In this sentence, biztonsági kód means security code.

In Hungarian, adjectives usually come before the noun, just like in English.

So:

• biztonsági kód = security code
• piros autó = red car
• nagy ház = big house

That is why biztonsági comes before kód.

No, not exactly.

• biztonsági = security-related / safety-related
• biztonságos = safe / secure

So:

• biztonsági kód = security code
• biztonságos hely = a safe place

This is an important difference.
In your sentence, biztonsági is the correct word because the code is not itself safe; it is a code for security.

A simple approximation is:

• Ez → like ez in beds, but shorter
• a → a short open vowel, roughly like o in British hot
• biztonsági → BIS-ton-shaa-ghi roughly
• kód → kohd

A few useful pronunciation points:

• Hungarian stress is usually on the first syllable of each word.
• s is pronounced sh
• sz is pronounced s
• ó is a long vowel

So the main stresses are:

• EZ a biZTONsági KÓD

Yes. This exact sequence of words can function as either:

• a noun phrase: this security code
• a full sentence: This is the security code.

Why? Because in Hungarian, the present-tense to be is often omitted in third person, so the sentence and the noun phrase can look identical.

Usually, context, intonation, and punctuation make the meaning clear.

For example:

• Ez a biztonsági kód. = full sentence
• Ez a biztonsági kód fontos. = here ez a biztonsági kód is clearly a noun phrase: This security code is important.

Because the sentence is talking about a specific code: the security code.

Hungarian marks definiteness with the article:

• a / az = the
• no article can often correspond to a/an in some contexts

So:

• a biztonsági kód = the security code

In this sentence, the speaker is pointing to a particular one, so the definite article is natural.

You would use az instead of ez:

• Az a biztonsági kód. = That is the security code.

Notice that the same pattern remains:

• ez a ... = this ...
• az a ... = that ...

So only the demonstrative changes.

Yes. Kód is a standard Hungarian word and is very commonly used.

Like many Hungarian words, it may ultimately be a borrowing, but for a learner it is best to treat it as a normal everyday Hungarian noun.

Examples:

• PIN-kód = PIN code
• titkos kód = secret code
• biztonsági kód = security code

So there is nothing unusual about using kód here.