Zod is a TypeScript-first schema declaration and validation library. It allows developers to define data shapes with a concise, readable syntax, automatically generating TypeScript types from these schemas. Zod validates data at runtime, catching inconsistencies and providing detailed error messages. This enables robust data validation for APIs, forms, and any application handling external inputs. Its focus on type safety reduces runtime errors and improves code maintainability, making it a valuable tool for ensuring data integrity in TypeScript projects.