1) The supplementation or replacement of natural speech and/or writing using aided and/or unaided symbols…The use of aided symbols requires a transmission device. 2) The field or area of clinical/educational practice to improve the communication skills of individuals with little or no functional speech.” Source: Lloyd, L.L., Fuller, D.R., & Arvidson, H.H. (1997) Augmentative and Alternative Communication: A handbook of principles and practices. Boston: Allyn and Bacon.