Change streams are a new feature in MongoDB 3.6 that enable applications to stream real-time data changes by leveraging MongoDB's underlying replication capabilities, providing a more efficient and secure way to process changes without the complexity or risk of polling the oplog. Change streams can be targeted to provide relevant and filtered changes to listening applications, resumable for cases where the connection is lost, and include majority-committed changes, ensuring durability in failure scenarios. They also provide total ordering, security, ease of use, and idempotence, making them a powerful tool for building real-time data processing applications, such as those used in trading, IoT, or dashboards.