"Orb Walking" expression is used for stoping orb animations on heroes who have orbs as attacks (like bone , viper, silencer, visage, obsidian etc ) . The points is that heros like those after attacking need some time to do next attack because of animation of orb. Ofcourse that will slow you much in chasing and let your opponents flee. ALso to do "orb walk" you need to single cast your orbs (not on autocast), on istance with silencer "w" and left click on your target. Next images will explain how to do it. Silencer is used as instance
The images above are instances of his attack. So when last instance finishes (red one) , you move your hero a bit (toward enemy if you chase) and go again "w" click ... Like that you will evade animation and hit much faster, because you will not be forced to w8 for silencer to spin his glaives .
NOTE* if you cast your orbs manually enemy creeps will NOT attack you , just as enemy tower, because its considered as spell. If you attack enemy hero normaly or with orb on autocast, creeps/tower will attack you
To make sure you'll understand:
*Credit to Eurobattle.net.