Despite the great advancements seen in medicine in recent years, fever of unknown origin (FUO) remains a serious diagnostic challenge. Regardless of the etiological elucidation in many cases of FUO and the progress seen in the management of these patients, there are currently many weaknesses in this area as a result of inconsistency in the definition and interpretation of key terminology and the utilization of different definitions and classifications. As a result, there is confusion among medical practitioners about FUO, which leads to laborious and difficult comparisons among different case series. This study outlines the mismatch in terminology and diversity found in the classification of the conditions that cause FUO and emphasizes the discrepancies between what some terminology intends to represent and what it actually represents in reality. Thus, we attempted to determine an appropriate solution for established inconsistencies.Keywords: Diagnostic approach, fever, fever of unknown origin, infection, neoplasm.