Widal Test (Slide Agglutination) is a rapid diagnostic test used to detect antibodies against *Salmonella* bacteria, which cause typhoid fever. In this test, a patient’s serum is mixed with antigens of *Salmonella* O (somatic) and H (flagellar) antigens. If antibodies are present, they cause agglutination (clumping), indicating infection. The slide agglutination method provides a quick result, but may not be as sensitive or specific as other methods. The Widal test is primarily used to diagnose typhoid fever, although cross-reactivity with other infections can lead to false positives.