Apache Accumulo is a distributed, scalable NoSQL database modeled after Google's Bigtable, designed to manage large amounts of unstructured data with dynamic configurations for data layout and security. The document outlines its architecture, which includes features such as automatic load balancing, dynamic partitioning, and a high-level Java API, along with effective data security measures and a lifecycle for managing data versions. Accumulo is capable of handling trillions of records while providing fast query responses and supports various applications through its unique data model and iterator functionalities.