Mount Everest
Mount Everest has the highest altitude( altitude is measured in feet above sea level). It is 8850m or 29,035 ft high above sea level. Other mountains maybe taller (being taller means " the total vertical distance between the base and summit of the mountain) but none is as high as mount everest above sea level. This makes Mount Everest, "the mountain with the Highest Altitude".
Mauna Kea
Mauna Kea is the tallest mountain in the world. It is 10,000+ meters above the sea