The FCC has a requirement for most RF devices to undergo compliance testing to meet their compliance rules for electromagnetic interference (EMI). In Wi-Fi, especially in tri-band systems with 2.4, 5, and 6 GHz, strict rules apply to band edges with steep cutoffs to preserve interference with adjacent spectrums (see FCC Equipment Authorization—RF Device).
A troublesome offshoot of radio-frequency (RF) technology is EMI. RF interference (RFI) is unique to a particular RF spectrum and a narrowband phenomenon, while EMI is applicable to the entire electromagnetic spectrum and a broadband phenomenon.