Termenul de retur se termină vineri.

Because -ul is the definite article attached to the end of the noun in Romanian.

• termen = a term / a deadline / a period
• termenul = the term / the deadline / the period

Romanian usually puts the definite article at the end of the noun, unlike English, which uses a separate word (the).

In this sentence, termen means something like deadline, time limit, or allowed period. In context, termenul de retur means the return period or the deadline for returns.

So even though termen can sometimes look similar to English term, here it is better understood as deadline / limit / period.

de retur means for return or of return, depending on how naturally you would say it in English.

This is a common Romanian structure:

• termen de plată = payment deadline
• termen de livrare = delivery term / delivery time
• termen de retur = return period / return deadline

So de + noun is often used to show what kind of term or deadline it is.

Because a se termina is the usual way to say to end / to come to an end when something finishes.

• Termenul se termină = The period ends
• X termină ceva = X finishes something

So:

• se termină = ends / comes to an end
• termină by itself often means finishes something

The se here is part of the verb expression and is very common in Romanian.

termină is 3rd person singular, present tense of a se termina.

It matches termenul, which is singular:

• termenul = singular
• se termină = it ends

So the sentence literally works like The return period ends Friday.

In Romanian, days of the week are often used without a preposition when meaning on Friday, on Monday, etc.

So:

• vineri = Friday / on Friday
• luni = Monday / on Monday
• marți = Tuesday / on Tuesday

That is why vineri by itself is perfectly normal here.

Yes, depending on context, vineri can mean either:

• on Friday (a specific Friday)
• on Fridays / every Friday (habitual meaning)

In this sentence, the meaning is clearly on Friday, because it refers to a specific deadline ending.

Yes. In natural English, The return period expires Friday or The return deadline is Friday can fit the meaning well.

In Romanian, another common verb would be expiră:

• Termenul de retur expiră vineri.

That sounds a bit more formal or administrative.
se termină is slightly more general: ends / comes to an end.

Yes. Romanian word order is flexible.

For example:

• Termenul de retur se termină vineri.
• Vineri se termină termenul de retur.

Both are correct. The first one is more neutral. The second puts more emphasis on Friday.

A rough guide for an English speaker:

TER-me-nul de re-TUR se ter-mi-NĂ VIN-eri

A few helpful points:

• ă is a very short, neutral vowel, like the a in sofa
• r is usually rolled or tapped
• u is pronounced like oo in food
• vineri is roughly VEE-ne-ree, though the Romanian i sounds are shorter and lighter

If you wanted to talk about multiple return periods, you would say:

Termenele de retur se termină vineri.

Breakdown:

• termenul = the term / the period
• termenele = the terms / the periods

The verb se termină stays the same in the present tense for 3rd person singular and plural in this case, so the change is mainly in the noun.

Yes, it is natural and correct. It sounds like something you might see in a store policy, on a website, or in customer service communication.

Depending on style, Romanians might also say:

• Termenul de retur expiră vineri.
• Perioada de retur se termină vineri.

But your sentence is perfectly standard.