Deeplearning4J is an open-source, distributed deep learning library written for Java and Scala. It provides tools for training neural networks on distributed systems. While large companies can distribute training across many servers, Deeplearning4J allows other organizations to do distributed training as well. It includes libraries for vectorization, linear algebra, data preprocessing, model definition and training. The library aims to make deep learning more accessible to enterprises by allowing them to train models on their own large datasets.