Welcome to RR.com! I am going to assume your question has to do with somewhere in Kentucky...I am the Kentucky forum moderator...feel free to ask your question with your city/county in which you are inquring about in the Kentucky forum below and someone will help you out there!
Thanks!
Marshall KE4ZNR
TAC Channels are used to keep primary channels clear.
If you hear a conversation referring to TAC 4, it's the agency's "TAC 4" channel. On the trunked systems, the talkgroup tag will be TAC 4, and on a conventional system, the channel's alpha tag here in RR may say TAC-4.