suppose one server is connected to 4 clients connecting 
with switch.so all the 5 terminals are called broadcaste
domain. and only 4 clients machines are called collision 
domain.

Broadcast Domain:--When Ever one Computer Are Sending A 
Broadcast message in the Network And If Another Computer 
Receive That Broadcast message, in that Case We Can Say 
Both Computer Belongs To Single Broadcast Domain.

Collision Domain:--When Ever Two Computer Are Sending a 
Message to Each Other at a Same Time, Then Collision Will 
Be Happen, in that case we can Say Both Computer belongs to 
Single Collision Domain.