To head out, get away, avoid or to fake out.
Originating in Canada: the shortening of decoy.
Most often used to describe how a hockey player will fake out the goaly then get around him.
Other uses involve getting away from or avoiding someone; leaving someplace for instance, a party; and getting out of the way; say to the countryside (we used to describe driving out of the city to various deking spots and smoking pot)
We scored a bag and deked out of the party to one of out favorite smoking spots on the mountain overlooking the city.