Fault tolerance is the attribute of a system that allows it to maintain a specified level of performance or functionality in the presence of faults. It represents a core concept and research domain in systems engineering and computer science. This field investigates methodologies for designing systems capable of detecting, isolating, and recovering from errors arising from hardware or software failures, thereby ensuring continued operation. Key characteristics explored include reliability, availability, and resilience to unexpected conditions. Its significance is paramount in the design of critical systems where dependability and uninterrupted service are essential.