query on port speed specification

Hi All,

In CSMA/CD Ethernet, what actually 100Mbps means:

1. Whether it is the Tx speed of that port. If so, whether it can support the same rate in Rx also at the same time.

1. Whether it is the speed on PHY device. But i have read like, a PHY can support 10,100 and 1000.

2. Or whether it is the speed of MAC.

1. How does this relate to MII interface speed.

I am a student. Please ignore this mail if it is very silly.

Thanks for your time, Ragi Paul