SINless refers to a person lacking a System Identification Number, either due to social status, species, or necessity. Squatters, illegal immigrants, and the poor are often SINless due to their low social status, and thus aren't able to gain lawful employment or equal rights. Certain sentient species are not given SINs, like shapeshifters and spirits. Shadowrunners and those in criminal syndicates tend to be SINless out of convenience, as it prevents the law from tracing crimes back to them.
On rare occasions, the SINless are given the opportunity to gain a legal SIN. For example, one of Dunkelzahn's Will bequests gave the Draco Foundation the authority to bestow one thousand SINs on the first one thousand SINless metahumans to show up on a certain date at their Seattle offices. More commonly, criminals and shadowrunners acquire illegal SINs to complete a forged identity with the help of a decker or government contacts.