What does "coup de théâtre" mean?
I saw four options for a multiple question on my french exercise book. They are:
A. coup de sifflet
B. coup de grâce
C. coup de foudre
D. coup de théâtre

I only understand the C. In fact, i am very confused about the meaning of "coup", what does it exactly mean? Especially since the right answer of this question is D, what is the meaning of D?

Thank you in advance for your kindly answer!

Question

What does "coup de théâtre" mean?
I saw four options for a multiple question on my french exercise book. They are:
A. coup de sifflet
B. coup de grâce
C. coup de foudre
D. coup de théâtre

I only understand the C. In fact, i am very confused about the meaning of "coup", what does it exactly mean? Especially since the right answer of this question is D, what is the meaning of D?

Thank you in advance for your kindly answer!

Answer

The A is when you blow the whishtle.
The B is when you shoot somebody with a bullet in the head to be sure that the person is well dead and don't suffer any more. You can see that after an execution.
The C is when you fall in love at first sight.
The D is when there is a sudden reversal especially in a play or a movie.

The word "coup" means something brief and strong. So you can figure out the meaning in each of those idioms. Un coup is also a punch (coup de poing) or a kick (coup de pied).