الوصف مهم.

• الوصف = the description
• مهم = important

So the sentence means The description is important.

Grammatically, this is a very common Arabic sentence type: noun + adjective/predicate.

In Arabic, the verb to be in the present tense is usually not written or spoken in simple sentences like this.

So:

• الوصف مهم literally looks like the description important
• but it means The description is important

This is completely normal in Arabic.
If you want was or will be, Arabic does use verbs, but for simple present-tense statements, it usually does not.

الـ is the Arabic definite article, equivalent to the in English.

So:

• وصف = description / a description
• الوصف = the description

Because the sentence is talking about a specific or definite description, الـ is used.

In this sentence, مهم is the predicate: it tells you something about الوصف.

In Arabic nominal sentences like this, the first noun is often definite, and the predicate is often indefinite:

• الوصف مهم = The description is important

If you said الوصف المهم, that would usually mean the important description, not a complete sentence.
That would be a noun phrase, not The description is important.

So:

• الوصف مهم = a full sentence
• الوصف المهم = the important description

It is pronounced approximately al-waṣf.

A few useful notes:

• الـ is pronounced al- here
• the و is w
• the ص is an emphatic s sound, often written ṣ
• the final ف is f

Also, the ل in الـ is pronounced here because و is a moon letter, not a sun letter.

So the article stays clear: al-waṣf, not something like aw-waṣf.

مهم is pronounced approximately muhimm.

The two م letters create a doubled m sound. In fully vowelled Arabic, this is shown with a shadda:

• مُهِمّ

So you should hear it as something like:

• mu-himm

not just mu-him.

In fully vocalized, formal Arabic, the sentence would be:

• الوَصْفُ مُهِمٌّ

These endings show nominative case:

• الوصفُ = subject/topic of the sentence
• مهمٌّ = predicate

In normal everyday writing, these case endings are usually omitted, so you simply see:

• الوصف مهم

That is completely standard.

It is adjective-like in meaning, but in this sentence it functions as the predicate of the sentence.

So:

• الوصف = the subject/topic
• مهم = what is being said about it

In English grammar terms, you can think of it as a predicate adjective:

• The description is important

So yes, مهم means an adjective (important), but in this sentence its role is the predicate.

Yes. When an adjective or predicate describes a noun in Arabic, it normally agrees with it in gender and number.

Here:

• الوصف is masculine singular
• so مهم is also masculine singular

For example:

• القصة مهمة = The story is important
  because القصة is feminine singular, so مهمة is feminine singular too.

Yes, Arabic sometimes allows different word order, but الوصف مهم is the most straightforward and neutral way to say it.

This is the standard pattern:

• subject + predicate

So:

• الوصف مهم

A different order can be used in some contexts for emphasis or style, but for learners, this basic order is the best one to learn first.

It is a nominal sentence.

Arabic sentences are often divided into two main types:

• verbal sentences: start with a verb
• nominal sentences: start with a noun

Since الوصف is a noun and the sentence begins with it, الوصف مهم is a nominal sentence.

This is one of the most common sentence patterns in Arabic.