Mountpoint for Amazon S3 is a new open-source file client that enables Linux-based applications to directly connect to S3 buckets using file APIs. It allows mounting S3 buckets on compute instances, presenting objects as local files and translating file system calls to S3 REST API calls. Mountpoint offers high single-instance throughput for faster job completion and reliable scaling across thousands of instances. It's ideal for large-scale workloads processing petabytes of data using read operations and sequential writes, such as machine learning training and genomics analysis. The video demonstrates how to use Mountpoint to access S3 buckets as a local file system, showcasing its seamless integration with standard Linux commands and business-specific tools.