هذه وجبة خفيفة.

هذه means this for a feminine singular noun.

The noun وجبة (meal) is grammatically feminine, so Arabic uses the feminine demonstrative:

• هذا = this (masculine)
• هذه = this (feminine)

So:

• هذه وجبة... = This is a meal...

You cannot use هذا with وجبة in correct Modern Standard Arabic.

In Arabic, many nouns are feminine because they end in ة (called tāʾ marbūṭa).

وجبة ends in ة, so it is treated as feminine:

• وجبة = meal

That is why words referring to it or describing it also appear in feminine form, such as:

• هذه = this (feminine)
• خفيفة = light (feminine)

So the gender agreement in the sentence is completely regular.

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

So:

• هذه وجبة خفيفة literally looks like this light meal
• but it means This is a light meal

This is very normal in Arabic.
If you wanted a past tense meaning, then Arabic would use a verb, for example:

• كانت هذه وجبة خفيفة = This was a light meal

Because Arabic adjectives normally come after the noun they describe.

So:

• وجبة خفيفة = a light meal

This is the normal order in Arabic:

• noun + adjective

Compare:

• كتاب جديد = a new book
• سيارة سريعة = a fast car
• وجبة خفيفة = a light meal

English usually puts the adjective first, but Arabic usually puts it after the noun.

Adjectives in Arabic must agree with the noun they describe in:

• gender
• number
• definiteness
• case

Since وجبة is feminine singular, the adjective must also be feminine singular:

• وجبة = meal
• خفيفة = light

If the noun were masculine, you would use the masculine form:

• طعام خفيف = light food

So خفيفة is feminine because it describes the feminine noun وجبة.

In English, we often say this is a light meal, where a light meal is indefinite. Arabic works similarly here.

So:

• هذه = this
• وجبة خفيفة = a light meal

The noun after the demonstrative does not have to be definite in this kind of sentence, because وجبة خفيفة is the predicate: it tells you what this is.

So the sentence structure is basically:

• هذه = subject
• وجبة خفيفة = predicate

Meaning:

• This is a light meal

In fully vocalized Modern Standard Arabic, yes. You would normally see:

• هذهِ وجبةٌ خفيفةٌ

Why?

• وجبةٌ is indefinite and nominative
• خفيفةٌ is an adjective matching it, so it is also indefinite and nominative

But in everyday writing, short vowels and tanwīn are usually omitted, so you commonly see:

• هذه وجبة خفيفة

Both represent the same sentence; the second is just unvocalized.

A careful MSA pronunciation is approximately:

• hādhihi wajbatun khafīfatun

In normal unvocalized reading, learners often say something closer to:

• hādhihi wajba khafīfa

A few pronunciation notes:

• هذه = hādhihi
• وجبة = wajbah / wajba
• خفيفة = khafīfah / khafīfa
• خ is the Arabic sound kh, like the ch in German Bach or Scottish loch

Not necessarily. خفيفة literally means light, but in context it can suggest different things, such as:

• not heavy
• small
• easy to digest
• not a full meal
• possibly low in richness or quantity

So وجبة خفيفة is often best understood as:

• a light meal
• sometimes a snack
• sometimes a small meal

The exact nuance depends on context.

Sometimes, but not always.

• وجبة خفيفة literally means light meal
• In many situations, that can function like snack
• But it can also mean a small, light meal rather than a typical snack

So depending on context, it could refer to:

• a snack between meals
• a small lunch
• a simple meal that is not heavy

If the meaning shown to the learner is This is a light meal, then that is the safest core meaning.