Electronic – a USB transceiver

The terminology is vague at best. There are no hard and fast rules, and nobody playing police when people don't use the term correctly.

Usually, but not always, a transceiver is a simple buffer that has different signal standards on the inputs and outputs. For example, an RS-232 transceiver usually interfaces TTL signals to RS-232 signals. Also, transceivers are similar to "drivers" and "receivers" except that a transceiver usually does both driver and receiver functions in the same chip.

A Phy is similar to a transceiver in that there is usually different signal standards on "both sides of the chip". With Ethernet it is MII/GMII/etc on one side and, well, Ethernet on the other. There are other Phy's that talk USB, PCIe, and many others. Phys usually incorporate some sort of SERDES (SERializer-DESerializer) function and line encoding. More sophisticated PHYs contain a mini-DSP in them to do all sorts of crazy communication things like advanced baseband wander correction.

A transceiver does not have to be associated with a serial data-- they can be used for parallel data as well. A PHY usually involves some sort of serial data stream. But this is more of a convention than a rule, and I am sure there are chips out there that are exceptions to this.

A host device is a computing device into which you can plug a peripheral.

Some micros can be either a host or a peripheral. Using the mouse as an example: If your micro is emulating a mouse and plugged into a computer, it is a peripheral. If your micro is accepting input from a mouse (and presumably acting on it in some way), then your micro is a host device, capable of hosting a plugged in peripheral.

Hopefully this makes sense.