These types of fats are called polyunsaturated fats. One popular form of polyunsaturated fats is found in cooking oil such as olive oil.
While vegetable oils and margarines are high in polyunsaturated fats they don't contain omega 3 fatty acids, also known as Essential Fatty Acids (EFAs).
These fatty acids are considered essential because they're important building blocks for every cell in your body. Your body can't produce these special fats so you must get them from your diet.