L forms, also known as L-phase variants, refer to bacterial cells that have lost their cell walls. These cells maintain their inner membrane, leading to the formation of irregular shapes. Synonymous terms for L forms include L-phase bacteria and cell wall-deficient bacteria. L forms can occur naturally, but they can also be induced under specific laboratory conditions. These cell wall-deficient bacteria are of great interest in microbiology and medical research, as they possess distinct characteristics and can exhibit unique behaviors. Further understanding of L forms and their relationship with typical bacterial forms holds potential in developing therapies against bacterial infections and exploring the evolution of microorganisms.