Alternate/Backup Port

Backup and alternative ports are port roles in RSTP.
Alternative port is port in discarding state and it is just another potential path to the root bridge. If some of the currently active paths to the root bridge becomes unavailable port will change state to forwarding and become new designated port or root port depending on what link on your topology drawing gets broken.
Backup port is port in discarding state that is connected to the shared network segment (like hub - so you will rarely see these today).

You can read Cisco's explanation - Understanding Rapid Spanning Tree Protocol (802.1w)

It is more interesting with this topology:

I forgot to mention above - backup port is always located on switch with designated port (as it can be seen on above picture (taken from Juniper site)).

Craig Beck

This is theoretical guys, just for learning and understanding how STP works.  :-)

Correct..

It is hard to Master one thing while you are doing Other things

Well, Alternate Port is just Blocking Port in STP
The gray area is the Backup Port, since HUBs are no longer used nowadays... Just thought to throw this question to see if Backup Ports are used in any other scenario than HUBs

If you turn off STP on one Switch that is connected to another switch with 2 links. the other Switch will have one Forwarding Port and one Backup Port. Because when you turn off STP on a Switch , it will operate as a HUB

Although HUB are not used today, some inexpensive switches don't support STP so the will produce loops within a network just like a HUB.

Additionally, to really function as HUB also ports on the switch should be configured in half duplex mode (forgot it above and comment is not editable anymore).

So to Make a Switch works as a HUB.
-Turn off STP
- execute this command : no mac address-table learning vlan #
-configure each connected port to be Half Duplex

Yes.
MAC address learning can be also disabled per port:
no mac-address-table learning interface <type> <port>

Thank you Guys !