What does << do? [duplicate]

What does << do? [duplicate]

References

Reference NO 1

https://edmv-ddl.dot.state.nc.us/DuplicateDriverLicense/DuplicateDLFAQ.html

Reference NO 2

http://www.dmv.ny.gov/licdup/ldpfaq.htm

Reference NO 3

https://servicearizona.com/webapp/driver/duplicate/showInfoPage.do

Reference NO 4

http://www.dmvnv.com/dlduplicate.htm

Reference NO 5

https://support.google.com/mail/answer/165334?hl=en

Reference NO 6

http://www.dmv.ri.gov/registrations/titles/

Reference NO 7

https://help.aweber.com/entries/21696783-What-Does-AWeber-Do-With-Duplicate-Subscribers-

Reference NO 8

http://kb.mailchimp.com/article/does-mailchimp-check-for-duplicates-when-i-import-my-list