Is there any resources could show me about debian accounts and groups spec?

[斟酌鵬兄 <tgckpg@gmail.com>]

There are tons of accounts and groups in /etc/passwd.and /etc/groups
Several account I'd already know what they do, but some like "bin, sys, lp. .."
How exactly they do good for system?

I've searched for google but couldn't identify the keywords

daemon:x:1:1:daemon:/usr/sbin:/bin/sh
bin:x:2:2:bin:/bin:/bin/sh
sys:x:3:3:sys:/dev:/bin/sh
sync:x:4:65534:sync:/bin:/bin/sync
games:x:5:60:games:/usr/games:/bin/sh
man:x:6:12:man:/var/cache/man:/bin/sh
lp:x:7:7:lp:/var/spool/lpd:/bin/sh
mail:x:8:8:mail:/var/mail:/bin/sh
news:x:9:9:news:/var/spool/news:/bin/sh
uucp:x:10:10:uucp:/var/spool/uucp:/bin/sh
proxy:x:13:13:proxy:/bin:/bin/sh
www-data:x:33:33:www-data:/var/www:/bin/sh
backup:x:34:34:backup:/var/backups:/bin/sh
list:x:38:38:Mailing List Manager:/var/list:/bin/sh
irc:x:39:39:ircd:/var/run/ircd:/bin/sh
gnats:x:41:41:Gnats Bug-Reporting System (admin):/var/lib/gnats:/bin/sh
nobody:x:65534:65534:nobody:/nonexistent:/bin/sh
libuuid:x:100:101::/var/lib/libuuid:/bin/sh
Debian-exim:x:101:103::/var/spool/exim4:/bin/false
statd:x:102:65534::/var/lib/nfs:/bin/false
messagebus:x:103:106::/var/run/dbus:/bin/false
avahi:x:104:107:Avahi mDNS daemon,,,:/var/run/avahi-daemon:/bin/false
sshd:x:105:65534::/var/run/sshd:/usr/sbin/nologin
saned:x:108:115::/home/saned:/bin/false
penguin:x:1000:1000:Penguin,,,:/home/penguin:/bin/bash
colord:x:106:117:colord colour management daemon,,,:/var/lib/colord:/bin/false
usbmux:x:110:46:usbmux daemon,,,:/home/usbmux:/bin/false
pulse:x:111:119:PulseAudio daemon,,,:/var/run/pulse:/bin/false
rtkit:x:112:121:RealtimeKit,,,:/proc:/bin/false
gdm:x:113:122:Gnome Display Manager:/var/lib/gdm:/bin/false
Debian-gdm:x:114:123:Gnome Display Manager:/var/lib/gdm3:/bin/false

-- 
Regards,
Panguin