Selective calling is the ability to be able to make:
Nearly all digital radios and some high-end analogue radio have Selective Calling features.
Selective calling allows you to split your radios into Groups. Each radio user normally only hears callers from their own Group and not calls from other Groups. This makes for quieter radios with only traffic relevant to a particular user being heard. This is called Group Calling, calls to and from the radios own or 'Home Group'.
One Group will usually have the ability to call any of the other Groups and a radio user may wish to call All radios, an 'All Call'. They can do this too.
A supervisor may wish to make a Private call to just one user / radio without anyone else hearing the call. This is also possible with Selective calling because each radio has a unique ID.