Apache Spark is an open-source, unified analytics engine designed for large-scale data processing and a cornerstone of the Big Data ecosystem. It improves upon earlier frameworks like Hadoop MapReduce by performing computations in-memory, resulting in significantly faster performance for a wide range of workloads. Spark's versatility is a key feature, offering a single platform for batch processing, interactive queries (Spark SQL), real-time analytics (Structured Streaming), machine learning (MLlib), and graph processing (GraphX). By providing high-level APIs in languages such as Python, Scala, and Java, it empowers data scientists and engineers to efficiently build complex data pipelines and analyze massive datasets distributed across clusters of computers.