هذا مفهوم جديد.

In Arabic, the present tense of to be is usually not expressed.

So:

• هذا مفهوم جديد literally looks like this concept new
• but it means This is a new concept

This kind of sentence is called a nominal sentence in Arabic.
If you wanted was, will be, etc., Arabic would use other words, but in the simple present, Arabic normally leaves is/am/are out.

هذا means this and is the masculine singular demonstrative.

In this sentence, it points to مفهوم because مفهوم is a masculine singular noun.

So the structure is:

• هذا = this
• مفهوم جديد = a new concept

Together: This is a new concept.

It is usually pronounced hādhā.

Arabic nouns have grammatical gender, and مفهوم is masculine.
Because of that, the demonstrative must match it:

• هذا = this for masculine singular
• هذه = this for feminine singular

So you say:

• هذا مفهوم جديد = This is a new concept
• but with a feminine noun, you would normally use هذه

Agreement is very important in Arabic.

Because in Arabic, adjectives normally come after the noun they describe.

So:

• مفهوم جديد = literally concept new
• natural English translation: a new concept

This is the standard adjective position in Arabic.

Because the phrase is indefinite: a new concept, not the new concept.

In Arabic, indefiniteness is often shown by the absence of الـ.

So:

• مفهوم جديد = a new concept
• المفهوم الجديد = the new concept

In your sentence, the meaning is indefinite, so both the noun and the adjective are indefinite.

Because Arabic adjectives must agree with the noun they describe in several ways, including definiteness.

Since مفهوم is indefinite, جديد must also be indefinite.

Compare:

• مفهوم جديد = a new concept
• المفهوم الجديد = the new concept

So the adjective copies the noun’s definiteness.

It is a full sentence.

More specifically, it is a nominal sentence made of:

• هذا = the topic / subject-like element
• مفهوم جديد = the predicate / what is being said about it

So the sentence is complete and natural in Arabic.

In fully vocalized Arabic, it would usually be written:

هَذَا مَفْهُومٌ جَدِيدٌ

Here:

• هَذَا = hādhā
• مَفْهُومٌ = mafhūmun
• جَدِيدٌ = jadīdun

Both مفهوم and جديد are typically nominative here, and when fully marked, they take ـٌ.

In normal everyday writing, these short vowels are usually omitted, so you usually just see:

هذا مفهوم جديد

Because Arabic usually leaves out short vowels and tanwīn in ordinary text.

So although the fully vocalized form is:

• مفهومٌ جديدٌ

you will normally see:

• مفهوم جديد

Learners often need to remember that the grammatical endings are still understood even when they are not written.

Usually, no. In normal MSA, this sentence is understood as:

This is a new concept.

If you want to say this new concept, Arabic would normally make the noun phrase definite, for example:

• هذا المفهوم الجديد

That means this new concept or this is the new concept, depending on context.

So the absence of الـ in مفهوم جديد helps show that your original sentence means This is a new concept.

The pattern is:

demonstrative + indefinite noun + adjective

Here that is:

• هذا = demonstrative
• مفهوم = noun
• جديد = adjective

This is a very common Arabic pattern for saying things like:

• This is a good book
• This is an important idea
• This is a difficult question

So this sentence is a useful model to remember.