Something major is big, big, big! It's major, baby! It's large! Important! Intense! Powerful! Michael Jackson's album "Thriller" was major, eventually becoming the biggest-selling album of all time.
A victory of 98 to 3 might well be called major. If you're a musician, you're probably also familiar with the difference between a minor scale and a major scale. A major scale sounds happy, while a minor one sounds sad. The discovery of life on another planet? Major. Getting into the college of your choice? Major. For everything else, there's "ordinary."