The Gran Sport name has been used on several high-performance cars built by Buick since 1965. In the GM brands hierarchy, Buick was surpassed in luxury and comfort appointments only by Cadillac, which did not produce performance models. As a result, the Buick GS series were the most opulently equipped GM sport models of their era.
(description text adapted from https://en.wikipedia.org/wiki/Buick_Gran_Sport)