A semantic layer acts as the Rosetta Stone for business users to understand complex datasets by translating raw technical language into understandable vocabulary and providing a unified view across the organization. The recent explosion of interest in Large Language Models (LLMs) has opened up exciting possibilities for automating data analysis and decision-making through AI Agents, but simply feeding raw database schemas to an LLM is a recipe for disaster due to the lack of understanding of meaning and context. A semantic layer with an LLM is indispensable for building enterprise-grade AI Agents focused on data analytics, providing essential business context that enables accurate interpretation of data. The layer's inherent nature as a knowledge graph encodes domain knowledge and business logic, defining concepts, relationships, and rules that the AI Agent uses to make sense of the world. A semantic layer typically includes a compiler that can translate simplified requests into executable SQL queries for seamless data interaction with underlying data warehouses. By providing a centralized framework that defines key metrics and business logic, embeds metadata, and offers business context, a semantic layer ensures accurate results, makes recommendations, and delivers on its promise. The benefits of using a semantic layer extend beyond preventing hallucinations to include consistency and governance, context for smarter decisions, improved performance and scalability, and AI preparedness.