هذا التصرف غريب.

In Arabic, simple present-tense sentences often do not use a verb meaning is/are.

So:

• هذا التصرف غريب literally looks like:
• this behavior strange

But it means:

• This behavior is strange

This is called a nominal sentence in Arabic. The idea of is is understood automatically in the present tense.

If you wanted a past tense, you would usually add a verb, for example:

• كان هذا التصرف غريبًا = This behavior was strange

هذا means this for a masculine singular noun.

In this sentence, التصرف is a masculine singular noun, so هذا is the correct demonstrative.

So the structure is:

• هذا = this
• التصرف = the behavior / the action / the conduct
• غريب = strange

Because التصرف is masculine singular, you use هذا, not هذه.

In Arabic, grammatical gender is not the same as biological sex.

A noun can be grammatically masculine or feminine even if it refers to a thing, idea, or action.
التصرف is grammatically masculine, so Arabic uses:

• هذا التصرف = this behavior

If the noun were feminine, you would use هذه instead.

For example:

• هذه الفكرة غريبة = This idea is strange

After a demonstrative like هذا, Arabic commonly uses a definite noun.

So:

• هذا التصرف = this behavior not usually:
• هذا تصرف

The noun is definite because you are pointing to a specific thing: this behavior.

This pattern is very common:

• هذا الكتاب = this book
• هذا الرجل = this man
• هذا التصرف = this behavior

Because غريب is not acting here as an attributive adjective inside a noun phrase like the strange behavior.
Instead, it is the predicate of the sentence: it tells us something about هذا التصرف.

So the sentence is:

• هذا التصرف = the topic / subject
• غريب = the comment about it

That is why غريب is normally indefinite.

Compare:

• هذا التصرف غريب = This behavior is strange
• هذا التصرف الغريب = this strange behavior

In the second one, الغريب is an adjective directly describing التصرف, so it becomes definite too.

It is originally an adjective, meaning strange or odd, but in this sentence it functions as the predicate of the nominal sentence.

So grammatically, it is describing the subject, but it is not just sitting next to the noun as part of one noun phrase. It completes the sentence:

• هذا التصرف = this behavior
• غريب = is strange

So you can think of it as:

• an adjective in meaning
• a predicate in sentence function

A careful pronunciation would be:

• hādhā at-taṣarruf gharīb

A few useful notes:

• هذا = hādhā
• التصرف is written with الـ, but because ت is a sun letter, the l sound of الـ is absorbed, so it is pronounced at-taṣarruf, not al-taṣarruf
• غريب = gharīb

So the whole sentence sounds like:

• hādhā at-taṣarruf gharīb

Because ت is one of the sun letters in Arabic.

When الـ comes before a sun letter, the l sound is not pronounced. Instead, the following consonant is doubled.

So:

• written: التصرف
• pronounced: at-taṣarruf

You still write الـ, but in speech the l disappears.

Compare:

• القمر = al-qamar because ق is a moon letter
• التصرف = at-taṣarruf because ت is a sun letter

In fully vocalized Standard Arabic, it would normally be:

• هٰذا التصرّفُ غريبٌ

Here is why:

• هٰذا is a demonstrative and does not change like a normal noun
• التصرّفُ has -u because it is the subject/topic of the nominal sentence
• غريبٌ has -un because it is an indefinite predicate

In normal modern writing, these endings are usually omitted, so you usually see:

• هذا التصرف غريب

التصرف is a noun. In this sentence it means something like:

• behavior
• conduct
• way of acting
• action

It comes from the root ص ر ف, which is connected with meanings like turning, directing, managing, or acting. In actual usage, تصرّف often means a person’s behavior or action in a particular situation.

So:

• هذا التصرف غريب = This behavior is strange or
• This action is strange

Normally, هذا means this, not that.

So the standard meaning is:

• هذا التصرف غريب = This behavior is strange

If you wanted that behavior is strange, you would usually say:

• ذلك التصرف غريب

That said, in some real-life contexts, translations can shift a little depending on what sounds natural in English, but grammatically هذا is definitely this.

You would change the demonstrative and make sure the adjective matches the noun’s gender.

For example, with الفكرة (the idea), which is feminine:

• هذه الفكرة غريبة = This idea is strange

Notice the changes:

• هذا → هذه
• غريب → غريبة

Arabic adjectives must agree with the noun in gender.

In Modern Standard Arabic, you could say:

• هذه التصرفات غريبة

Breakdown:

• هذه = these / this feminine
  (Arabic commonly uses هذه with non-human plural nouns)
• التصرفات = the behaviors
• غريبة = strange

A key point: with non-human plurals, Arabic often treats them grammatically like feminine singular for agreement. So even though التصرفات is plural, the adjective is often غريبة, not a masculine plural form.

The difference is mainly specificity.

• هذا التصرف غريب = This behavior is strange
• التصرف غريب = The behavior is strange or Behavior is strange, depending on context

With هذا, you are pointing to a specific behavior, almost like saying this particular action.

Without هذا, the sentence is less explicitly demonstrative. It may still refer to a specific behavior already known from context, but it no longer means this.

Yes, depending on context.

غريب can mean:

• strange
• odd
• unusual
• weird

In a neutral learning context, strange is often the safest translation.
If the tone is more informal or stronger, weird may fit well.

So هذا التصرف غريب could be translated as:

• This behavior is strange
• This is strange behavior
• This behavior is weird

The best choice depends on tone and context.