Despite metal oxides offer excellent characteristics in the field of photocatalysis, they often suffer from charge carrier recombination as well as limited visible response, which indeed reduce the charge kinetics process and ultimately reduce the photocatalytic output. Defect engineering is a sophisticated technique to manufacture defects and alter the geometric structure and chemical environment of the host. The present study provides an all-inclusive outline of recent developments on the classification of metal oxide defects based on the dimensions of a host crystal lattice. Precisely, surface modification of metal oxides through 0D (point), 1D (line), 2D (planar), and 3D (volume) defects with their subsequent mechanism and impact on photocatalytic performance are presented. By wisely amending the morphology (cores along with the shells) and electronic structure of metal oxide photocatalysts (TiO2, ZnO, Bi2O3, Fe2O4 etc.) through different attuned and veritable approaches, their photocatalytic activity can be substantially improved. Optimal studies on defect engineering not only expose the altered physicochemical features but also modulate the electron-hole pair dynamics, stability, and active radical production for various photoredox reactions. Altered atomic, as well as electronic configuration, facilitated a photocatalyst material to have different optical features, adsorption properties along with improved carrier transfer as well as isolation rate. Thus, the systematic exploration of photocatalytic rudiments of defect rich metal oxide for various applications such as H2 evolution, CO2 reduction, pollutant degradation, and bacterial disinfection could bring significant research advancement in this field.