Perioada de probă începe luni.

A natural word-by-word breakdown is:

• perioada = the period
• de probă = of trial / probationary / for testing
• începe = starts / begins
• luni = Monday

So the whole phrase is literally something like The trial period starts Monday, which is why it is translated as The probation period starts Monday.

Because perioada is the definite form: the period.

In Romanian, the definite article is usually attached to the end of the noun, instead of being a separate word like English the.

• perioadă = a period
• perioada = the period

So:

• O perioadă de probă = A probation period
• Perioada de probă = The probation period

Romanian often expresses ideas like this with a noun + de + noun structure.

So:

• perioadă de probă literally means period of trial/testing
• in natural English, that becomes probation period or trial period

This is very common in Romanian. A few similar patterns are:

• sală de sport = gym (literally room of sport)
• mașină de spălat = washing machine
• ochelari de soare = sunglasses

So de probă is not unusual at all; it is a normal Romanian way to describe the type or purpose of something.

Because after de in this kind of expression, Romanian usually uses the basic indefinite noun form.

Here:

• probă = trial / test
• de probă = for trial / probationary / test-related

You are not saying of the trial here. You are describing what kind of period it is.

Compare:

• perioadă de probă = probation period
• perioada de probă = the probation period

The definiteness is carried by perioada, not by probă.

Because începe is the 3rd person singular present form of a începe = to begin / to start.

The subject is Perioada de probă, which is singular:

• perioada = singular
• so the verb must also be singular: începe = starts

A quick comparison:

• Perioada începe = The period starts
• Perioadele încep = The periods start

So începe agrees with the singular subject.

Romanian often does not need a preposition where English uses on with days of the week.

So:

• începe luni = it starts Monday / on Monday
• plec marți = I’m leaving Tuesday / on Tuesday
• vin joi = I’m coming Thursday / on Thursday

This is completely normal Romanian.

You may also see other time expressions with prepositions, but with days of the week after verbs like start, come, leave, work, etc., no preposition is very common.

Here it means Monday.

The form luni can sometimes be ambiguous if taken by itself, because context matters. But in this sentence, the most natural reading is clearly a single upcoming day:

• Perioada de probă începe luni = The probation period starts Monday

If Romanian wants to make a repeated, habitual meaning clearer, it often uses forms like:

• lunea = on Mondays
• în fiecare zi de luni = every Monday

So in your sentence, luni is understood as Monday, not Mondays.

Because in Romanian, the days of the week are normally written with lowercase letters, not capitals.

So:

• luni = Monday
• marți = Tuesday
• miercuri = Wednesday

This is different from English, where Monday must be capitalized.

Romanian only capitalizes it if it comes at the beginning of a sentence or for a special stylistic reason.

A simple learner-friendly guide:

• începe ≈ in-CHE-pe
• probă ≈ PRO-buh

A few useful pronunciation notes:

• î is a Romanian vowel that does not really exist in English. It is a close central sound; learners usually approximate it at first.
• ce in începe sounds like che in check
• ă in probă is like the weak vowel in about

So începe is roughly in-CHE-pe, not in-SEE-pe.

Yes. Romanian word order is fairly flexible.

These are both natural:

• Perioada de probă începe luni.
• Luni începe perioada de probă.

The difference is mainly one of emphasis:

• Perioada de probă începe luni focuses first on the probation period
• Luni începe perioada de probă highlights Monday

Both mean the same basic thing.

Yes, very much so.

In work and HR contexts, perioada de probă is the standard Romanian expression for:

• probation period
• trial period

So this is not just a literal combination of words; it is also a common set phrase you will see in contracts, job descriptions, and workplace communication.