Rucsacul este greu.

In Romanian, the definite article is usually attached to the end of the noun.

• rucsac = backpack / a backpack
• rucsacul = the backpack

So -ul is the masculine/neuter singular definite article here.

This is different from English, where the comes before the noun.

Because the base noun is rucsac. When Romanian adds the definite article, it keeps the whole noun and adds -ul:

• rucsac → rucsacul

Nothing is removed. The final c is part of the original word.

Este means is. It is the 3rd person singular form of the verb a fi (to be).

So:

• rucsacul = the backpack
• este = is
• greu = heavy

Yes. E is a very common short form of este in everyday Romanian.

So both are correct:

• Rucsacul este greu. = a bit more full/formal/neutral
• Rucsacul e greu. = very common in speech

Because greu is a predicate adjective here: it describes the subject through the verb to be.

This works much like English:

• The backpack is heavy.

Romanian uses the same basic pattern:

• Rucsacul este greu.

Romanian adjectives change form to agree with the noun in gender and number.

Rucsac is a neuter noun. In Romanian, neuter nouns behave:

• like masculine in the singular
• like feminine in the plural

Since rucsacul is singular, the adjective takes the masculine singular form:

• greu = masculine/neuter singular
• grea = feminine singular

So Rucsacul este greu is correct.

It is neuter.

That can be confusing for English speakers, because English nouns usually do not have grammatical gender. In Romanian, neuter nouns act:

• masculine in the singular
• feminine in the plural

So:

• singular: un rucsac greu / rucsacul este greu
• plural: două rucsacuri grele / rucsacurile sunt grele

A rough English-friendly pronunciation is:

rook-SAH-kool ES-teh greh-oo

A few notes:

• u is usually pronounced clearly, not reduced like English unstressed vowels
• r is trilled or tapped
• eu in greu forms a diphthong, something like eh-oo said smoothly together
• g in greu is a hard g, like in go

This is only an approximation, but it is a useful starting point.

No. Romanian does not need a dummy subject like English it in this sentence.

English says:

• It is heavy or The backpack is heavy

Romanian simply says:

• Este greu = It is heavy / It’s heavy (if the context is clear)
• Rucsacul este greu = The backpack is heavy

The noun itself is enough; no extra pronoun is needed.

Yes, but Rucsacul este greu is the normal, neutral order.

You may also hear:

• Greu e rucsacul.
• Este greu rucsacul.

These can sound more marked, emphatic, or context-dependent. For a learner, the safest default is:

• Rucsacul este greu.

Add nu before the verb:

• Rucsacul nu este greu. = The backpack is not heavy.

In everyday speech, you will also hear:

• Rucsacul nu e greu.

You would remove the definite article:

• Un rucsac este greu. = A backpack is heavy.

More naturally, depending on context, Romanian might also say:

• Un rucsac e greu.

So the key contrast is:

• rucsac = backpack / a backpack
• rucsacul = the backpack