Networking professionals often interchange the terms port and interface, and we have purposely done so to this point. In the Trellix IPS context, however, there is an important distinction to be made; a port actually represents the physical component, whereas an interface represents the logical abstraction of one or more ports.
A simple example of the difference between port and interface is with regard to a "port pair." When you configure a Sensor to run inline, you combine and manage two physical ports as a single logical interface.
A sub-interface is a further abstraction of an interface. It allows an administrator to apply different scanning policies to different types of traffic flowing through the same interface.