Replica este scurtă.

Because Romanian usually puts the definite article at the end of the noun instead of using a separate word before it.

So:

• replică = a reply / a line
• replica = the reply / the line

This is very common in Romanian:

• casă = house
• casa = the house

So Replica este scurtă uses a noun with the definite article already attached.

Replică is the basic, indefinite form of the noun.
When it becomes definite singular, it changes to replica.

For many feminine nouns ending in -ă, the definite singular form ends in -a:

• replică → replica
• masă → masa
• scrisoare works differently, but the idea is the same: the article is attached to the noun

So replica means the reply / the line, while o replică means a reply / a line.

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

So:

• Replica = the reply / the line
• este = is
• scurtă = short

A very common shorter spoken form is e:

• Replica e scurtă.

That means the same thing and is very natural in everyday Romanian.

Because Romanian adjectives must agree with the noun in gender and number.

Replica is a feminine singular noun, so the adjective must also be feminine singular:

• masculine singular: scurt
• feminine singular: scurtă
• masculine plural: scurți
• feminine plural: scurte

So:

• un răspuns scurt = a short answer
• o replică scurtă = a short reply

In your sentence, replica is feminine singular, so scurtă is the correct form.

Yes. Replică is feminine.

You can tell from the article and adjective agreement:

• replica = definite feminine singular
• scurtă = feminine singular adjective

If the noun were masculine, the adjective would look different. For example:

• răspunsul este scurt = the answer is short

So the form of scurtă helps confirm that replica is feminine.

Very often, yes. Romanian commonly places descriptive adjectives after the noun:

• o replică scurtă = a short reply
• un drum lung = a long road

So Replica este scurtă follows a very normal Romanian pattern.

Romanian can sometimes put the adjective before the noun, but that often sounds more emphatic, literary, or changes the nuance.

Usually, no—not in a normal complete sentence like this.

Romanian generally keeps the verb to be in ordinary statements:

• Replica este scurtă.
• Replica e scurtă.

If you say only Replica scurtă, it sounds incomplete in most contexts, like a note title or a fragment rather than a full standard sentence.

So for normal speech, use este or e.

A simple learner-friendly pronunciation is:

reh-PLEE-kah ES-teh SKOOR-tuh

A few helpful points:

• replica is stressed on pli: re-PLI-ca
• este is usually ES-te
• scurtă is stressed on the first syllable: SCUR-tă

The Romanian ă is a short neutral vowel, similar to the a in English sofa.

So in scurtă, the last vowel is not a clear a like in father. It is weaker and more central.

Because they are different word forms.

The noun comes from replică, but in the definite singular it becomes replica.
So the final ă changes when the definite article is attached.

By contrast, scurtă is simply the feminine singular form of the adjective scurt, and that form normally ends in -ă.

So:

• replică = an indefinite noun form
• replica = the definite noun form
• scurtă = feminine singular adjective form

It normally refers to a specific reply or line, because replica is definite: the reply / the line.

So the sentence most naturally means something like:

• The reply is short.
• That line is short.

If you wanted an indefinite idea, you would normally use:

• O replică este scurtă. = A reply is short.

But that sounds less natural unless you are making a general statement in a special context. The definite form in your sentence points more naturally to a particular reply or line.

Yes, Romanian word order is somewhat flexible, but Replica este scurtă is the most neutral and standard order.

You may also hear:

• Replica e scurtă. — same meaning, more everyday
• Scurtă este replica. — more emphatic or literary

For a learner, the safest pattern is:

noun + form of a fi + adjective

So Replica este scurtă is the best basic version to remember.