/System/Library/Frameworks/ApplicationServices.framework/Versions/A/Frameworks/SpeechSynthesis.framework/SpeechSynthesis The Speech Synthesis Manager, formerly called the Speech Manager, is the part of macOS that provides a standardized method for Mac apps to generate synthesized speech. For example, you may want your application to incorporate the capability to speak its dialog box messages to the user.
The binary is a part of ApplicationServices public framework.