Shorts that only go down to your knee (maybe shorter).
Back in the day, people wouldn't have their shorts down to their ankles like people do now.
Haven't you seen old school ballers from the NBA? Their shorts would be at their knee caps or shorter.
About the example: When Nas first got into the rap game, with the album 'Illmatic' back in 1994, people weren't wearing these huge over-sized shorts that some people do now.
When Nas hit the scene I was still rockin knee-highs - The Game on 200 Bars and Runnin
By Ursulina
Knee-high
Similar to "back in the day". Usage signifies that you have known said person for a long time; technically since you were little kids who were only as tall as the lower leg of an adult. Your height was "knee high".
Aaron: Hey man, that kid Sam is a real chiller. How do you know him?
Ben: He's been my boy for a while. I know that kid from knee-high