It means the no. of holes on the sprockets, through which the Nut Bolts are attached, to join it to rear wheel.
For example, Bajaj Pulsar 180 UG3 has 4 holes in its' sprocket, from which the 4 couples of Nut & Bolt are fixed, and its attached to the wheel...
This is generally 2 for the front sprocket, as its a smaller one...
