Flat elliptical polymer particles and use thereof

These flat elliptical polymer particles have a front view, a planar view, and a side view in a projection diagram based on third-angle projection which are all elliptical. The flat elliptical polymer particles satisfy (1)-(4): (1) the average length (L AV ) of flat portions satisfies 0.13 ≤ (L AV ) ≤500 µm; (2) the average breadth (D AV ) of the flat portions satisfies 0.1 ≤ (D AV ) ≤ 250 µm; (3) the average (P1 AV ) aspect ratio (L/D) calculated from the length (L) and the breadth (D) satisfies 1.3 < P1 AV ≤ 50; and (4) the average (P2 AV ) aspect ratio (D/T) calculated from the breadth (D) and the thickness (T) of the side surface satisfies 1.2 < P2 AV ≤ 100.