id command outputs

I always write the following statement. I am learning Linux from Christopher Negus's Linux Bible. When I am providing id command then along with my uid, gid and groups some other information are also coming like
Code:4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),120(lpadmin),131(lxd),132(sambashare)From a source on internet I have found that
Quote:

adm Monitor system logs cdrom Use CD-ROM drives lpadmin Configure printers sudo administer the system, ... sambashare Share files with the local network dip Connect to the Internet using a modem plugdev Access external storage devices

How numbers are chosen and what do they mean beside each such element within bracket. Like 24(cdrom Use CD-ROM drives) what is the actual meaning?