Learn French: L'orage a éclaté pendant que je regardais la télévision. - The storm broke while I was watching television.

This is the classic pattern for a background action interrupted by a sudden event. Je regardais (I was watching) sets the ongoing background scene. L'orage a éclaté (The storm broke) is the specific, sudden event that happens in the middle of it, so it takes the passé composé.

Does a éclaté literally mean the storm exploded?

Basically, yes! The verb éclater means to burst, smash, or explode. In French, un orage éclate is the most common way to say a storm broke or started suddenly, usually with a crash of thunder.

Why is it pendant que instead of just pendant?

You use pendant que (while) when it is followed by a full clause with a subject and a verb, like je regardais here. You use just pendant (during) when it is followed only by a noun, for example: pendant l'orage (during the storm).

Could I use quand (when) instead of pendant que in this sentence?

Yes, you could say quand je regardais la télévision (when I was watching television). Both are grammatically correct, but pendant que strongly emphasizes the duration of the background action, making it the perfect fit to show the two things overlapping.