Apache Ignite is an in-memory platform that can accelerate Hadoop and Spark workloads by storing data in memory. It provides a distributed in-memory file system (IGNITE) that can be used as a secondary storage layer for Hadoop. For Spark, Ignite allows sharing RDDs across jobs by storing them in an Ignite cache, avoiding the need to write to disk between jobs. The IgniteContext class provides the main entry point for integrating Spark and Ignite, allowing Spark jobs to read from and write RDD data directly to Ignite caches.