Cum fabula finita esset, plausus magnus ex auditoribus ortus est.

Here cum introduces a subordinate clause and most naturally means when or after:

Cum fabula finita esset = when/after the play (or story) had ended

Latin cum can have several meanings depending on context:

• when
• since
• although

In this sentence, the sense is clearly temporal: first the performance/story ends, then the applause begins.

Esset is the imperfect subjunctive of sum.

In a cum clause referring to past circumstances, Latin very often uses the subjunctive, not the indicative. So:

• cum ... esset = when ... had been / when ... was

More specifically, finita esset is part of a pluperfect passive subjunctive form:

• finita esset = had been finished / had ended

A learner might expect an indicative after when, because English uses one, but Latin often prefers the subjunctive after cum in this kind of past narrative sentence.

It is a verb phrase made of:

• finita = perfect passive participle of finio
• esset = imperfect subjunctive of sum

Together they form the pluperfect passive subjunctive:

• fabula finita esset = the play/story had been finished

Yes, finita looks like an adjective, and in form it behaves like one, agreeing with fabula:

• fabula = feminine singular nominative
• finita = feminine singular nominative

But here it is not merely descriptive. With esset, it becomes part of a finite verb expression.

Because fabula is the subject of esset, so it is in the nominative, not the ablative.

An ablative absolute would look more like:

• fabula finita only if both words were ablative — but fabula in the ablative would be fabula, while finita in the ablative feminine singular would also be finita, so the form alone could look similar

What tells you this is not an ablative absolute is the presence of the finite verb esset. This is a full subordinate clause:

• cum fabula finita esset = when the play had ended

So this is a cum clause, not an ablative absolute.

It could mean either in isolation, because fabula can mean:

• story
• fable
• play/drama

But the rest of the sentence strongly suggests play or performance, because we then get:

• plausus magnus
• ex auditoribus ortus est

That is, great applause arose from the audience/listeners. Applause from an audience fits a dramatic performance very naturally.

So in context, fabula is most likely play.

Plausus is nominative singular, and it is the subject of ortus est.

It means applause, clapping, or cheering.

So:

• plausus magnus = great applause

One thing that can confuse learners is that plausus is a 4th-declension noun, so its nominative singular ends in -us, but it is not a 2nd-declension noun.

Because magnus agrees with plausus, which is masculine nominative singular.

So:

• plausus = masculine nominative singular
• magnus = masculine nominative singular

If it were modifying a neuter noun, then magnum would be possible. But here it must match plausus.

Ex means out of, from, or from among, and it takes the ablative case.

So:

• auditoribus = ablative plural of auditor
• ex auditoribus = from the listeners / from the audience

A very natural English translation is simply:

• from the audience

Even though auditoribus is literally plural (listeners), English often uses singular collective nouns like the audience.

Because Latin is thinking in terms of the individual people listening:

• auditor = listener
• auditoribus = listeners (ablative plural)

English often prefers the collective idea:

• the audience

So the Latin is more literally from among the listeners, while good English may say from the audience.

Ortus est is the perfect tense of the deponent verb orior, meaning to arise, to spring up, to begin.

Deponent verbs are important because:

• they have passive-looking forms
• but active meanings

So:

• ortus est does not mean was arisen
• it means arose or has arisen

Thus:

• plausus magnus ... ortus est = great applause arose ...

This is a very common source of confusion for English-speaking learners.

The dictionary form is orior, oriri, ortus sum.

Its principal parts are usually given as:

• orior = I arise
• oriri = to arise
• ortus sum = I arose / have arisen

Because it is deponent, its perfect system uses the participle + forms of sum, just as passive verbs do in form.

Latin word order is much more flexible than English word order, because case endings show how words relate to one another.

This sentence is arranged quite naturally for Latin:

• subordinate clause first: Cum fabula finita esset
• main clause after it: plausus magnus ex auditoribus ortus est

Latin often places important or vivid words in emphatic positions. Here:

• Cum fabula finita esset sets the scene first
• plausus magnus comes early in the main clause, giving prominence to the applause
• ortus est comes at the end, a very common place for the verb

English usually needs a more fixed order, such as:

• When the play had ended, great applause arose from the audience.

Yes. Because the verb in the cum clause is effectively pluperfect in sense, the action is completed before the main verb:

• first, the play ended
• then, the applause arose

So both of these are reasonable:

• When the play had ended, great applause arose from the audience.
• After the play had ended, great applause arose from the audience.

When is more literal for cum, but after often expresses the sequence very clearly in English.

Yes, in form it is passive:

• finita esset = had been finished

But in English, with something like a play or story, we often prefer an active-style translation:

• the play had ended

That sounds more natural than:

• the play had been finished

So the Latin form is passive, but idiomatic English may use a more natural active expression. This is very common in translation: we translate the meaning naturally, not always word-for-word.

Yes. A very literal translation would be:

When the play had been finished, great applause arose from the listeners.

That is grammatically close to the Latin.

A more natural English version would be:

When the play had ended, great applause arose from the audience.

Or even:

After the play ended, loud applause broke out from the audience.

All of these reflect the same Latin structure, but some are more idiomatic in English than others.