The explorer's grand slam is a really big challenge for people who like to explore and be adventurous. It's like a big game where you have to climb to the top of the highest mountains and go to the North and South Pole.
First, you have to climb the highest mountain in the world, called Mount Everest. It's really really tall and hard to climb, but if you make it to the top, you get to check off one box on your explorer's grand slam list.
Next, you have to climb the tallest mountain in each of the seven continents. So that means you have to climb a lot of really tall mountains!
Then, you have to go to the North and South Pole. This means you have to travel to the very top and very bottom of the Earth, where it's really cold and snowy.
It's a really big challenge because climbing mountains is really hard and takes a long time. And going to the North and South Pole also takes a lot of planning and preparation. But if you complete the explorer's grand slam, you get to say that you did something really special and amazing!