CTCSS: Continuous Tone Controlled Squelch System
DCS: Digitally Controlled Squelch
Retevis calls both of these features "Privacy Codes".
Privacy Codes are not extra channels -- rather they are a means for sharing a channel with other people without any annoying interference or cross talk. Even though there may be other people using the channel, you will only hear transmissions from those people who are using the same Privacy Code as you.