accuracy with which an electronic system reproduces the sound or image of its input signal
"The new headphones boast exceptional fidelity, ensuring that every subtle nuance of the original recording is reproduced perfectly."
the quality of being faithful
"Her unwavering fidelity to her marriage made everyone in the community admire her character."
Faithfulness to one's duties.
"The nurse displayed great fidelity by staying late to ensure every patient received their medication on time."
In plain English: Fidelity is being loyal and faithful to someone, especially by staying true to them even when things get hard.
"Her fidelity to her husband never wavered despite years of temptation."
Fidelity entered English in the 15th century from Middle French and Latin, where it originally meant "faith" or "loyalty." The word is a doublet of fealty, sharing roots with the Proto-Indo-European verb meaning to trust or command.