Fidelity

In the 1950s, the terms "high fidelity" or "hi-fi" were popularized for equipment and recordings which exhibited more accurate sound reproduction.

In the 1976 edition of the Oxford Dictionary,[clarification needed] lo-fi was added under the definition of "sound production less good in quality than 'hi-fi'", and in the glossary of the 1977 book The Tuning of the World, was defined as "unfavourable signal-to-noise ratio".

In 2003, the Oxford Dictionary added a second definition: "A genre of rock music characterized by minimal production, giving a raw and unsophisticated sound."

In the field of program evaluation, the term fidelity denotes how closely a set of procedures were implemented as they were supposed to have been.

For example, it is difficult to draw conclusions from a study about formative assessment in school classrooms if the teachers are not able or willing to follow the procedures they received in training.