Consistency models are frameworks that define the behavior of data in distributed systems, ensuring that all users see the same data at the same time. They help manage how updates to data are propagated and perceived across different nodes in a network. Common models include strong consistency, where all reads return the most recent write, and eventual consistency, where updates will eventually propagate to all nodes, but may not be immediate. These models are crucial for applications that require reliable data access, such as cloud computing and database management systems. By choosing the appropriate consistency model, developers can balance performance and reliability based on the needs of their applications.