Why A folded dipole is a half-wave dipole with a second conductor of the same length running parallel to it and joined to it at both ends, forming a long thin loop fed at the center of one side. The current divides between the two conductors, which steps the feedpoint impedance up by a factor of four, roughly 280 to 300 ohms instead of about 70 ohms, so it matches 300 ohm twinlead directly or 50 ohm coax through a 4:1 balun. The two-wire construction also gives it a wider usable bandwidth than a single-wire dipole.
Watch out The description of ends folded down 90 degrees is closer to an inverted V or a bent/shortened dipole, and forward gain describes a directional array such as a Yagi; a folded dipole has essentially the same figure-eight pattern and gain as a plain dipole.
Folded = two parallel wires joined at the tips; impedance x4, about 300 ohms, and wider bandwidth.