A key-value store is a non-relational database that utilizes a hashtable or dictionary as its underlying data model. It uses a simple key-value method to store data, making it scalable and performant. SingleStore can be used as a key-value store on an application, offering advantages such as cost savings by using a single database, leveraging existing skills with SQL compatibility, simplifying architecture, and increasing speed with ultra-fast data ingestion and sub-second latencies. To use SingleStore as a key-value store, one needs to create a free database cluster, select the in-memory rowstore table, and define a schema that includes a primary key and hash index. The example demonstrates how to connect to the database using Node.js, insert and read data, and run performance tests. By using SingleStore as a key-value store, developers can simplify their architecture while maintaining high performance and scalability.