Key-Value Stores are databases that store data using unique keys associated with specific values. They enable rapid retrieval of data through these keys. This type of database is highly scalable and suitable for handling large volumes of data with simple queries. Unlike relational databases, Key-Value Stores don't require predefined schemas, providing more flexibility and speed but less complex query capabilities. Common applications include caching, sessions, and simple data models, similar but distinct from Document Stores and Graph Databases.