Fidelity is the quality of faithfulness or loyalty . Its original meaning Regarded duty in a Broader sense than the related concept of fealty . Both derive from the Latin word fidelis , meaning “faithful or loyal”. In the city of London financial markets it has been used in the sense of “My word is my bond”.
Fidelity also denotes how exactly a copy reproduces its source. For example, a worn gramophone I record will have a lower fidelity than one in good condition, and a recording made by a low budget record company in the early 20th century is likely to have significantly less audio fidelity than a good modern recording. In the 1950s, the terms ” high fidelity ” or “hi-fi” were popularized for equipment and recordings which exhibited more accurate sound reproduction. The converse term ” lo-fi “, does not necessarily mean “low fidelity”, rather than the production ethic “for gritty authenticity” over perfect production. Similarly in electronics, fidelity refers to the correspondence of the output signal to the input signal, rather than sound quality, as in the popular internet connection technology ” Wi-Fi “.
Scientific modeling and simulation
In the fields of scientific modeling and simulation , fidelity refers to the degree to which a model or simulation reproduces the state and behavior of a real world object, a feature or condition. Fidelity is therefore a measure of the realism of a model or simulation.  Simulation fidelity has been described in the past as “degree of similarity”.  In quantum mechanics and optics,  the fidelity of a field is calculated as an integral part of the field of interest with a reference or target field.
In the field of program evaluation , the term fidelity denotes how closely a set of procedures have been implemented. For example, it is difficult to draw conclusions from a study on the subject of assessment in school classrooms if the teachers are not able or willing to follow the procedures they received in training. 
- Jump up^ “SISO-REF-002-1999: Fidelity Implementation Study Group Report” . Simulation Interoperability Standards Organization. 1999 . Retrieved January 2, 2015 .
- Jump up^ Hays, RT; Singer, MJ (1989). Simulation fidelity in training system design: Bridging the gap between reality and training . Springer-Verlag.
- Jump up^ Bowman, D .; Harte, TL; Chardonnet, V .; Groot, C. De; Denny, SJ; Goc, G. Le; Anderson, M .; Ireland, P .; Cassettari, D. (2017-05-15). “High-fidelity phase and amplitude control of phase-only computer generated holograms using conjugate gradient minimization” . Optics Express . 25 (10): 11692-11700. ISSN 1094-4087 . arXiv : 1701.08620 . doi : 10.1364 / OE.25.011692 .
- Jump up^ O’Donnell, Carol L. (2008). “Defining, Conceptualizing, and Measuring Fidelity of Implementation and its Relationship to Outcomes in K-12 Curriculum Intervention Research”. Review of Educational Research . 78 (1): 33-84. doi : 10.3102 / 0034654307313793 .