First Originated From Del Boy In Only Fools And Horses. It Grew Popular Around London. As A Result Of Gangs Using It After Two Young Males, Jamie & Marcus Decided To Keep Saying It Till It Caught. Its Now Spread All Around The World.
It Basically Means - Cool
Marcus: We Are Going Pub If You Want To Come With Us
Jamie: Kooshty! Corse I Will
A person who is easy to bed
that girl is kooshty