Adjective. Of a body: thick and solid, although not necessarily fat. That is, nicely filled out and sensually appealing, voluptuous.
Of a woman: buxom and shapely, with broad hips and lots of sensuous, womanly curves (as opposed to a twiggy, androgynous, stick figureed waif)
Of a man: broad-shouldered and barrel-chested and often muscular (big and butch instead of a willowy pretty boy)
Kate Winslet, famously full-figured, once said "I'm not a twig and I refuse to be".
"Full-figured" does not mean "fat", per se, just a nicely filled and sensually shaped figure: nice, shapely legs; broad-shouldered and barrel-chested men; broad-hipped women generously endowed in the butt and breasts.