“Hit Me Hard and Soft,” her third album, is both concise and far-reaching. By Jon Pareles “Twenty-one took a lifetime,” Billie Eilish, 22, sings in “Skinny,” the song that opens her third album, “Hit Me Hard and Soft.” Any woman her age ...

Rihanna’s first album, Music of the Sun, was a success. It included two popular singles: “Pon de Replay” and “If It’s Lovin’ that You Want.” These singles both drew influence from Caribbean music, reflecting Rihanna’s Barbadian heritage.

The thing about soft rock is that it was never an exclusive genre. Cross-pollinating among pop, rock, country rock and, especially, adult contemporary music of the day, the best soft rock records spread their roots widely across genre lines and years.