deb http://mirrors.163.com/debian/ jessie main non-free contrib deb http://mirrors.163.com/debian/ jessie-updates main non-free contrib deb http://mirrors.163.com/debian/ jessie-backports main non-free contrib deb-src http://mirrors.163.com/debian/ jessie main non-free contrib deb-src http://mirrors.163.com/debian/ jessie-updates main non-free contrib deb-src http://mirrors.163.com/debian/ jessie-backports main non-free contrib deb http://mirrors.163.com/debian-security/ jessie/updates main non-free contrib deb-src http://mirrors.163.com/debian-security/ jessie/updates main non-free contrib
main consists of DFSG-compliant packages, which do not rely on software outside this area to operate. These are the only packages considered part of the Debian distribution.
contrib packages contain DFSG-compliant software, but have dependencies not in main (possibly packaged for Debian in non-free).
non-free contains software that does not comply with the DFSG.