Hi-Fi (English)

Japanese: Hi-Fi（英語表記）HiFi

… In the early days of audio, the technical level was low, and the primary goal was to improve the physical sound quality, so efforts were made to reduce noise and distortion and to expand the frequency band and dynamic range. This is where the term Hi-Fi (short for high fidelity) was born. High fidelity refers to the degree to which an input signal is faithfully transmitted and output in a transmission system. …

From [Records]

… One of the challenges that records as a medium have always pursued is the issue of high fidelity (Hi-Fi for short). However, this has been done in the midst of the conflicting task of so-called “reproduction of the original sound” and “creating sound” as a record. …

*Some of the terminology that mentions "Hi-Fi" is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

Japanese:

…　オーディオの初期のころは技術レベルが低く，物理的音質を向上させることが第1目的となり，雑音やひずみを減らし，周波数帯域やダイナミックレンジを広くする努力がなされてきた。ここにハイファイHi‐Fi(high fidelityの略)，すなわち高忠実度という用語が生まれた。高忠実度とは伝送システムにおいて入力信号を忠実に伝送して出力信号とする度合が高度であることを表す。…