هناك ثقب في الحائط.

In this sentence, هناك is being used in an existential way, so the whole beginning means there is.

Literally, هناك often means there or over there, but in sentences like this:

• هناك ثقب... = There is a hole...

So Arabic is using a word that literally points to a place, but in context it works like English there is / there are.

Because in Arabic, in the present tense, you usually do not use a verb equivalent to English is/am/are in simple sentences like this.

So:

• هناك ثقب في الحائط literally looks more like There a hole in the wall
• but the natural English translation is There is a hole in the wall

This is completely normal in Arabic.
If you wanted a past tense, then a verb would appear:

• كان هناك ثقب في الحائط = There was a hole in the wall

A simple way to understand it is:

• هناك = there is / there
• ثقب = hole
• في الحائط = in the wall

So the structure is:

• هناك + noun + prepositional phrase

More literally:

• There is + a hole + in the wall

This is a very common Arabic pattern for introducing the existence of something.

It is indefinite. In fully vocalized Arabic, it would be:

• ثُقْبٌ

The ـٌ ending shows indefiniteness and nominative case. But in normal everyday Arabic writing, short vowels and case endings are usually omitted, so you just see:

• ثقب

So even though you do not see the ending in ordinary text, the meaning is still a hole, not the hole.

A fully vocalized version would be:

• هُناكَ ثُقْبٌ في الحائِطِ

This helps show pronunciation and grammar:

• هُناكَ = hunāka
• ثُقْبٌ = thuqbun
• في = fī
• الحائِطِ = al-ḥāʾiṭi

In normal printed Arabic, you will usually see it without these vowel marks:

• هناك ثقب في الحائط

It is pronounced approximately:

• thuqb

More carefully in MSA:

• thuqbun when fully vocalized in this sentence

A few pronunciation notes:

• ث sounds like English th in think
• ق is a deep q sound, produced farther back than English k
• The word is short and compact: thuqb

So ثقب is not pronounced like saqab or thakab. The vowel is u, and the final consonant is q before b.

Arabic uses في here because the idea is that the hole is in the wall, not simply attached to it.

• في = in
• الحائط = the wall

This matches English quite well, since English also says:

• a hole in the wall

So this part is very direct and natural.

Because the sentence is referring to a specific wall, or at least to a wall understood from context.

• حائط = wall
• الحائط = the wall

Arabic often uses the definite article الـ where English also uses the. So:

• في حائط = in a wall
• في الحائط = in the wall

In your sentence, الحائط is definite, while ثقب is indefinite:

• ثقب = a hole
• الحائط = the wall

Because ح is a moon letter, not a sun letter.

In Arabic, the ل of الـ is:

• pronounced with moon letters
• assimilated (not clearly pronounced) with sun letters

Since ح is a moon letter, you pronounce the article clearly:

• الحائط = al-ḥāʾiṭ

Compare that with a sun-letter word like:

• الشمس pronounced ash-shams, not al-shams

So here the correct pronunciation keeps the l sound.

Not always. Literally, هناك often means there or over there, and it can suggest some distance. But in sentences like this, it is very commonly used just to mean there is / there are, without strongly emphasizing distance.

So in:

• هناك ثقب في الحائط

the main point is existence: There is a hole in the wall.

If you want, you can think of it as an idiomatic structure rather than a strictly spatial one.

Yes. That is also correct:

• يوجد ثقب في الحائط = There is a hole in the wall

This version uses the verb يوجد = there exists / exists.

A rough comparison:

• هناك ثقب في الحائط = very common existential pattern, natural and straightforward
• يوجد ثقب في الحائط = also standard and common, slightly more explicitly verbal

Both are good Modern Standard Arabic.

Yes, Arabic has some flexibility, but not every version sounds exactly the same.

The most natural sentence here is:

• هناك ثقب في الحائط

You may also encounter structures like:

• في الحائط ثقب

which is closer to In the wall is a hole, or There is a hole in the wall with focus on the location.

But for a learner, هناك ثقب في الحائط is the safest and most useful pattern to remember.

After a preposition like في, the following noun is in the genitive case.

So in full vocalization:

• في الحائِطِ

The final ـِ marks the genitive.

This is a very important rule in Arabic:

• في البيتِ = in the house
• على الطاولةِ = on the table
• من المدرسةِ = from the school

So in your sentence, الحائط is genitive because it comes after في.