A database schema is a blueprint that defines how data in a database is organized. It outlines the structure of the data and establishes relationships between different elements within the database. The schema is crucial for maintaining consistency, facilitating efficient querying, and ensuring data integrity. In SQL databases, schemas can also refer to named groups of database objects or visual representations of a database's structure. Designing an effective schema requires careful consideration of factors such as overall structure, naming conventions, constraints, data types, indexes, security, geo-partitioning, and documentation.