In plain English
DevOps brings together the work of building software and keeping it running. Teams coordinate changes, automate repeatable tasks such as testing and deployment, and use feedback from the live service to guide improvements. Responsibility extends from writing a feature to understanding how it behaves for customers.
Example
A startup's engineers use automated checks to test an update, release it in a container, and monitor errors afterward. The people who built the feature also help investigate production problems and improve the release process.