The port description is reported (and discovered by Smarts) in the portName OID (.1.3.6.1.4.1.9.5.1.4.1.1.4<port index>) of the CISCO-STACK-MIB. Cisco documentation describes the portName object as "a descriptive string used by the network administrator to name the port." The port description is string text as specified in the device configuration using the CLI.
An example of a port description is highlighted below in bold.
Name : "PORT-fixedcat2.manchester.switch.customer.net/4.5 [commserver14]"
In the Smarts AM Topology Browser, the port description text is added to the Port object name, which is browsable. Port objects can be viewed in the Topology Browser by expanding the following:
<class> --> <device> --> composedOf --> Port