DevOps started out as "Agile Systems Administration". In 2008, Andrew Shafer did a talk called "Agile Infrastucture" addressing issues around involving more of the company in the same disciplines as programmers.
In 2009, Patrick Debois created "DevOpsDays" conference to help to bring it to light. However, it wouldn't begin to trend until about 2010, when people would begin to describe it as a standalone discipline.
Today, DevOps goes beyond just developers, systems administration and infrastructure, its about [dev, ops, agile, cloud