Fidelity
Fidelity is a notion, that at its most abstract level implies a truthful connection to a source. It's original meaning dealt with loyalty to a lord or a king, which was derived from one's responsibility or duty.In recent times, fidelity has come to denote how accurate a copy is to its source. Recording media like vinyl records have a lower fidelity than digital files, for example.
Fidelity in a human relationship (mainly marriage) is generally held to mean monogamy and a lack of adultery.