(R-F-I)

Electronic devices emit radio waves to some degree. If those waves interfere with other devices you have RFI. Place an AM radio right next to an operating computer and tune through the dial; you may find some RFI. (In my student days, the early 1960s, we used to have fun by placing a radio next to the school mainframe and running programs that played tunes on the radio via RFI static.)

Most countries have some set requirements about the amount of RFI that can be emitted by various devices. This is to protect citizens (high levels of radiation can affect people) and other equipment (you don't want a computer to affect your television that sits next to it).