Cropping

Cropping an image lets you essentially recompose a photo by trimming away excess areas. You could also think of it as a way to zoom into a photo, almost as though your were increasing the focal length of a lens. The one drawback to doing this in post-production, rather than with a zoom lens, is that you lower the resolution of the photo as you do so. This will limit the size that you can print to, without sacrificing too much quality. However, this is only an issue if you camera has fewer than 12mp. It is certainly a very useful technique though if you are only using your photos to post to social media.

Generally, you would crop to the same aspect ratio as the original photo, but you are not limited to this. You could reshape your image too, making it square, or creating a more panoramic effect.