Infrared detector has been widely applied in aerospace reconnaissance, electro-optical countermeasures, and space science. Currently, it is undergoing a critical transition from the "full development of the third generation" to the "exploration of the fourth generation." Based on the pressing demands of current infrared detection applications, the preliminary definition and development considerations of the fourth-generation infrared detector was discussed. First, the developmental trajectory of infrared detectors was outlined. The evolution trend of the fourth-generation infrared detectors was explored from the perspectives of function integration, disciplinary advancement, and technology progression, and an initial definition for fourth-generation infrared detectors was proposed. Secondly, the preliminary contemplation on pivotal technological advancements for fourth-generation infrared detectors, encompassing the exploration of extreme detection performance, multidimensional light field information sensing, on-chip intelligence, and infrared microsystem chips, was delineated. Finally, an intelligent manufacturing ecosystem for infrared detectors was envisaged, which facilitates the transition of fourth-generation infrared detectors from conceptualization to practical application.