SQLite is a relational database engine written in C, distributed as a library embedded directly into an application, which stores the entire database in a single file and is queried with SQL. It needs no server to install or manage.
This lightness makes it one of the most widely deployed databases in the world: it is embedded in smartphones (iOS, Android), web browsers, many desktop applications and connected devices. Its code is in the public domain.
SQLite is ideal for local storage, mobile apps, testing and prototypes. It is less suited to many users writing at the same time, where a server such as PostgreSQL or MySQL is usually chosen. Some newer projects also use it server-side for lightweight applications.
Why it matters when hiring
SQLite carries little hiring weight on its own: most developers know it. It becomes a real topic for mobile and embedded developers, who have to handle schema migrations, sync and on-device performance. In that case, ask how the candidate handled a data migration on an app already in production.