Why is my NB5 "modem/router" described as such when it only has 1 Ethernet
port (and 1 USB port)?
A Modem. Is a device that bridges Between the general media signal ((cable
or telephone line) and your computer to bring in the Internet signal (Like a
door man between the outside traffic and the tenants in the building).
A Routing circuit is an electronic circuit that directs Internet connection
to few commuters using one shared connection (like a Cop directing traffic).
A switch is a device that acts as a center to connect few computers together
(like hallways that connect between rooms in the house).
A Combo Modem/Router put these three aspects into one plastic box.
In your case the switch part has only one RJ-45 port, and one USB port.
These combos are usually given for free by the ISPs to their subscriber a
one ort switch is less expensive than 4 ports.