Avtalevilkårene er tydelige.

It is a compound noun:

• avtale = agreement / contract
• vilkår = terms / conditions
• -ene = the definite plural ending

So avtalevilkårene is literally something like the agreement terms or the contract terms.

Compound nouns are very common in Norwegian, and they are usually written as one word, not several separate words.

In Norwegian, compound nouns are normally written as a single word. English often uses separate words where Norwegian prefers one compound.

So:

• agreement terms → avtalevilkår
• school bus → skolebuss
• winter coat → vinterjakke

If you split them up in Norwegian, it can sound unnatural or even change the meaning.

It is plural definite: the terms / the conditions.

Here is the pattern:

• et avtalevilkår = a contract term
• avtalevilkår = contract terms / contract conditions
• avtalevilkårene = the contract terms / the conditions of the agreement

A useful thing to notice is that vilkår often has the same form in singular indefinite and plural indefinite:

• et vilkår
• vilkår

Then the definite plural becomes vilkårene.

Because the noun is plural definite, and adjectives usually take -e in that situation.

Compare:

• et tydelig vilkår = a clear term
• tydelige vilkår = clear terms
• de tydelige vilkårene = the clear terms

In your sentence, the noun is already definite plural:

• Avtalevilkårene er tydelige.

So tydelige agrees with the plural noun.

Er is the present tense of å være (to be).

So:

• er = is / are

Norwegian uses the same present-tense form er for both singular and plural subjects:

• Avtalevilkåret er tydelig. = The contract term is clear.
• Avtalevilkårene er tydelige. = The contract terms are clear.

Unlike English, Norwegian does not change the present form of to be according to singular/plural in this way.

Because avtalevilkårene already contains the idea of the.

The ending -ene marks the noun as definite plural, so you do not need de here.

Compare:

• Avtalevilkårene er tydelige. = The contract terms are clear.
• De tydelige avtalevilkårene = the clear contract terms

In the second example, de appears because there is an adjective directly before the definite noun. That is part of Norwegian double definiteness.

The sentence follows a very common Norwegian pattern:

• Subject + verb + adjective

So:

• Avtalevilkårene = subject
• er = verb
• tydelige = predicate adjective

This is the same basic structure as in:

• Bilen er rød. = The car is red.
• Reglene er enkle. = The rules are simple.

Yes, that would normally be wrong.

Since avtalevilkårene is plural, the adjective should also be plural:

• Avtalevilkårene er tydelige. ✅

If the noun were singular, then you would use tydelig:

• Avtalevilkåret er tydelig. ✅

So the difference is:

• tydelig = singular / neuter singular predicate form
• tydelige = plural form

The singular version would be:

• Avtalevilkåret er tydelig.

Breakdown:

• avtalevilkåret = the contract term / the agreement condition
• er = is
• tydelig = clear

This is a good pair to study:

• Avtalevilkåret er tydelig. = The contract term is clear.
• Avtalevilkårene er tydelige. = The contract terms are clear.

Yes. The base noun is:

• et vilkår

That means it is a neuter noun.

Because the whole compound is built on vilkår, the compound is also neuter in the singular:

• et avtalevilkår
• avtalevilkåret

In Norwegian compounds, the last part usually determines the grammatical gender.

A learner-friendly approximation would be something like:

• AHV-tah-leh-vil-KOAR-neh air TY-deh-lee-geh

A few pronunciation notes:

• å in vilkår is a long vowel, somewhat like the vowel in British law
• -ene in vilkårene is pronounced clearly
• tydelige usually has a light, unstressed ending

If you want to sound natural, focus especially on the rhythm of the compound noun:

• avtale-VIL-kå-re-ne

Yes, that is possible.

Both avtale and kontrakt can be used in this kind of context:

• avtalevilkårene
• kontraktsvilkårene

The exact choice depends on style and context:

• avtale can feel a bit broader: agreement
• kontrakt can feel more specifically like a contract

But grammatically, the sentence works the same way in both cases.

It is a predicate adjective, not an adjective placed directly before a noun.

Compare:

• Avtalevilkårene er tydelige.
  Here tydelige comes after er and describes the subject.

• De tydelige avtalevilkårene
  Here tydelige comes before the noun and directly modifies it.

This matters because Norwegian adjective forms are often easier to understand when you notice whether the adjective is:

• predicative: after er/blir/virker etc.
• attributive: directly before the noun