I am reading these 2 questions and I do not understand the answers??
1) If a switch has 4 ports, how many broadcast domains does it have?
answer: 1
2) If a router has 4 ports, how many broadcast domains does it have?
answer: 4

My questions:
What does broadcast domain mean here?? is it physical port?? what is
the relation between the number of ports and the broadcast domain.

I do not understand why a switch with 4 ports has 1 broadcast domain??
and why the router with the same number of ports has 4 broadcast
doamins??

Thanks a lot..