What is an opening scene?

According to wikipedia, opening scenes introduce characters, plots, and settings, and where the story is going. Writers can take more time unpacking opening scenes than they can anywhere else in the story. The first and last scenes are almost always the ones authors can write with ease in a fully fleshed out way.

Also, these scenes are the most important of all as these are the first scenes or clips the audience sees and can leave a big impact or can be the most inevitable piece in a movie.