The remarkable achievement of using words to represent things usually begins around 12 months, but babies can vary by several months and still be in the normal range. These first words do not necessarily refer to things the child wants, because most babies have learned other strategies for getting people to do things for them. Usually, a baby’s first words refer to objects that interest him or her, like people, pets, or toys. Sometimes babies make up words to refer to things, and to a child these are “real” words. Also, children might use a single word for many different types of things; the word “dog” at first might refer to all animals that have four legs.
Bates, E., Bretherton, I., & Snyder, L. (1988). From first words to grammar: Individual differences and dissociable mechanisms. Cambridge, UK: Cambridge University Press.