Grand slam 是棒球中的术语,求他的英语解释.也就是大满贯-全垒打.

A grand slam is a home run hit with all three bases occupied by baserunners ("bases loaded"),thereby scoring four runs—the most possible in one play.
According to The Dickson Baseball Dictionary,the term was originated in the card game of contract bridge,in which a grand slam involves taking all the possible tricks.