What is DevOps?

I've heard a lot of waffling definitions of DevOps that left me with more questions than answers. A colleague explained it to me like this:

DevOps is where:

• Developers are responsible for getting code into production, and keeping it running. They receive problem alerts from production.
• Member of the Operations team attend Development team standups.
• When a problem arises, the two teams work closely together to resolve it

In contrast, seperate Dev and Ops is:

• The development team is treated like a third-party supplier, who delivers a fully working and documented application.
• When the software breaks they are still treated like a third-party supplier