Abbreviations (shortcuts, residues)
Structural abbreviations (Synonyms: shortcuts or residues) like NO2 for the Nitrogroup represent the most common use of Sgroups in the chemical representation. In the following example the blue section on the right is the Sgroup that is used for the Nitrogroup shortcut definition.
Note that the chemist drawing the abbreviation is responsible that the name corresponds to the underlying structure.
Abbreviations are very heavily used in the context of biologics to keep the structure readable like in the following peptide sequence. In these cases some of the abbreviation definitions are overlaying to each other to ensure the functionality of the peptide builders and other similar tools.