Apache Kafka is a distributed messaging system that allows for publishing and subscribing to streams of records, known as topics, in a fault-tolerant and scalable way. It is used for building real-time data pipelines and streaming apps. Producers write data to topics which are committed to disks across partitions and replicated for fault tolerance. Consumers read data from topics in a decoupled manner based on offsets. Kafka can process streaming data in real-time and at large volumes with low latency and high throughput.