"Obliques" is a term that refers to the muscles on both sides of the upper body. They are also called external abdominal oblique muscles. Obliques assist in turning the body from side to side. Any sport that requires twisting your torso also requires oblique strength for power (ie. golf, tennis, rowing, etc).
Obliques serve as stabilisers for your frame. In almost every physical activity such as compound lifting, the oblique muscles are engaged. It is therefore important to keep them strong.
Fun fact: You can get rid of "love handles" by workout out the obliques!
Unfortunately many tend to neglect working out the oblique muscles because it isn't part of the "six pack," which is what most people are after. Obliques are also not as visible as the rectus abdominus, and trying to make them visible takes a lot of effort and time. Nevertheless, well developed obliques actually enhance the look of the rest of the abdominals.
Obliques resistance bands exercises:
Getting rid of "love handles":