I confuse two technical term:
what is the different of them?
172.16.1.15 is the broadcast address for the subnet 172.16.1.0 /28. So any broadcast transmitted from any address between 172.16.1.1 - 14 will be switched to each NIC on that network.
Putting vlans aside for a second ... think about this in physical terms instead of logical terms. Think of every switchport as a collision domain. Think of each router port as a broadcast domain (and the switch tree below it). Collision domains make up broadcast domains.
With hubs, you have one collision domain extended out all ports. With switches, you can have multiple broadcast domains traversing one switch via different vlans ... but still, every port on a switch is a separate collision domain. With sub-interfaces on a router, you can have multiple broadcast domains residing on one physical interface.
Routers break up broadcast domains.
Switches extend broadcast domains.
Switches break up collision domains.
Hubs extend collision domains.