An oblong face, sometimes called long or rectangular, is distinctly longer than it is wide, with the forehead, cheekbones and jaw carrying fairly similar widths. There is no dramatic taper. The length is what stands out.
This is the shape most often confused with oval, and the difference is only one of degree. An oval runs about 1.38 times as long as it is wide. An oblong runs nearer 1.58. That gap is not obvious by eye but it changes the advice completely, because the two shapes need opposite things.
How to check whether this is your shape
Measure hairline to chin and the cheekbone width, then divide. Anything approaching 1.5 or above is reading long, and the oblong advice will serve better than the oval advice.
Check the three widths as well. On an oblong they sit reasonably close together, near 0.90 forehead and 0.84 jaw against cheekbone width. If one is dramatically different, the shape is heart, diamond or triangle instead.
Keep the camera level with your eyes. Shooting from below stretches the lower face and can push a genuine oval into oblong territory on the measurement alone.