Final answer:
President Donald J. Trump speaking with military service personnel is an example of mass communication, which is the transmission of information to large audiences via various channels, including the internet and television, used historically by presidents to conduct public relations.
Step-by-step explanation:
When President Donald J. Trump speaks with military service personnel on duty around the world, this is an example of mass communication. Mass communication is a process in which a person, group of people, or an organization sends a message through a channel of communication to a large audience. This does not require the audience to be in proximity to the communicator, and the communication is not typically interactive. An example of mass communication is the president using a televised address or the internet to reach a nationwide or global audience.
Throughout history, U.S. presidents have used various forms of media to communicate with the public. From President Franklin Roosevelt's radio fireside chats to President Barack Obama and President Donald Trump's use of social media platforms, each advancement in technology has provided presidents with new means to engage in public relations and spread their messages widely.