DevOps combines IT operations (responsible for the availability, operational stability, and continuity of software) and application development (responsible for innovation/change and leading new features/fixes as fast as possible into production) and is designed to prevent a common »blame game«: developers want to respond to requests from business departments and put new features into production, but IT operations sees this as jeopardizing availability.
It describes a shared understanding, mindset, and attitude designed to enable more effective and efficient collaboration between these involved departments/disciplines through common accountability, complementary goals, shared incentives, processes, and tools.
It improves the quality of the software, the speed of development, the frequency of delivery of the software, and the interaction between the involved departments/disciplines. The better the teams, tools, and infrastructure are aligned, the faster teams can deliver their software with better quality.