DynamoDB Accelerator (DAX) is an in-memory caching service designed to enhance the performance of Amazon DynamoDB. It allows applications to retrieve data from the cache rather than querying the database directly, which significantly reduces response times for read-heavy workloads. DAX is fully managed, meaning users do not need to worry about infrastructure management or scaling. It seamlessly integrates with existing DynamoDB applications, providing a simple API that allows developers to take advantage of caching without changing their code. This results in faster data access and improved application performance.