APCO Project 25
From The RadioReference Wiki
Overview
Project 25 trunked radio systems are so named because they follow the open APCO Project 25 standard for public safety trunked radio systems. Multiple vendors make and sell Project 25 systems and compliant radios. Audio on these systems is exclusively digital using the APCO-25 Common Air Interface (CAI) standard.
Motorola's implementation of the Project 25 digital trunking standard is marketed as "ASTRO-25."