A delay in the achievement of motor or mental milestones in the domains of development of a child, including motor skills, speech and language, cognitive skills, and social and emotional skills. This term should only be used to describe children younger than five years of age. The phenotype is Global developmental delay (HP_0001263). Also known as: Delayed cognitive development, Delayed development, Delayed developmental milestones, Delayed intellectual development, Delayed milestones, Delayed psychomotor development, Developmental delay, Developmental delay in early childhood.