The document discusses the classification and stages of gingivitis. It describes gingivitis as being classified based on duration into acute or chronic, and based on distribution into localized, generalized, marginal, or papillary. It then outlines the four stages of gingivitis: initial lesion, early lesion, established lesion, and advanced lesion. It provides details on the clinical and microscopic features of each stage. The document also discusses changes in the position of the gingiva that can occur during disease, such as coronal migration (pseudopockets) or apical migration (recession).