Speech generating devices (SGD), also known as voice output communication aids (VOCA), are electronic augmentative and alternative communication

Augmentative and alternative communication

Augmentative and alternative communication is an umbrella term that encompasses the communication methods used to supplement or replace speech or writing for those with impairments in the production or comprehension of spoken or written language...

 (AAC) systems that enable individuals with severe speech impairment to verbally communicate their needs.

Speech generating systems may be dedicated devices developed solely for AAC, or non-dedicated devices such as computers that run additional software to allow them to function as AAC devices.
SGDs are important for people who have limited means of communicating verbally, as they allow individuals to become active participants in communication interactions.