Specific language impairment (SLI) is diagnosed when a child's language does not develop normally and the difficulties cannot be accounted for by generally slow development, physical abnormality of the speech apparatus, autism spectrum disorder, acquired brain damage or hearing loss.
Perfect competition. A perfectly competitive market is a hypothetical market where competition is at its greatest possible level. Neo-classical economists argued that perfect competition would produce the best possible outcomes for consumers, and society.
A niche market simply involves the buying or selling of specific product or services to a targeted market. It does not involve providing services to everyone; rather, it focuses on selling products and services that meet the need of a particular kind or segment of people.