In 2004, Yeh and Cantor introduced high-entropy alloys (HEAs), which maximize configurational entropy by utilizing nearly equal elemental molar ratios. These HEAs are valuable for exploring the central regions of phase diagrams. Building on this concept, Rost et al. proposed entropy-stabilized oxides in 2015, revealing that high-entropy oxides (HEOs) exhibit structural stability driven by entropy. This article provides a comprehensive overview of HEOs, with a specific focus on high-entropy oxide ceramics (HEOCs). The paper explores the origins of the high-entropy concept and the fundamental effects of high-entropy materials. It examines entropy from its basic definition and investigates microscopic atomic distribution, crystal-level distortions, and electronic structures. Additionally, the article introduces theoretical prediction methods applied to high-entropy materials. Furthermore, this review systematically summarizes HEOCs, encompassing three key aspects: crystal structure, preparation methods, and performance applications. Finally, the review concludes by proposing future research directions based on the current progress in HEOCs.