There are two main categories of dwarfism. One category is disproportionate dwarfism, meaning that the person has some average-size parts of the body, such as the head and/or trunk, and some shorter-than-normal parts of the body, such as the legs and arms. The most common type of disproportionate dwarfism is achondroplasia. In fact, achondroplasia acounts for about 70 percent of all cases of dwarfism.
The other main category of dwarfism is proportionate dwarfism, meaning that the person is small all over. Growth-hormone deficiency dwarfism, primordial dwarfism, and Seckel syndrome are types of proportionate dwarfism. In the past, a person who was very small was called a "midget" (a term now considered offensive and derogatory).