There are numerous synonyms for the term "extremely high frequencies." Some common ones include microwave frequencies, radio frequencies, super high frequencies, very high frequencies, ultra-high frequencies, and gigahertz frequencies. These are all terms referring to electromagnetic waves that have shorter wavelengths and higher frequencies than common AM and FM radio waves. Extremely high frequencies are used in various applications such as satellite communication, radar systems, and medical imaging equipment. Regardless of the term used, these frequencies have revolutionized various industries by enabling faster communication, more precise and efficient detection, and diagnosis of medical conditions.