Song

In the case of wiki terminology, a "song" is simply a non-single that can be considered an album track or any other song that has not been commercially released as single.

Promotional single
Promotional singles are singles that have not been released "officially" and are mainly used to promote the parent album or simply be released as a stand-alone release. Promotional singles, in the case of the URAPS music industry, are usually radio-only singles or digital-only singles but are not official physical singles (in other words, these songs don't usually get added to main release schedule but can go for adds on radio and can be released digitally).