Definition
An ORM (Object-Relational Mapper) is a library that translates between database rows and in-memory objects. Instead of writing raw SQL (SELECT * FROM users WHERE id = 42), you work with code (db.user.findUnique({ where: { id: 42 } })), and the ORM generates, escapes, and executes the SQL for you. Popular ORMs include Prisma and TypeORM (JavaScript/TypeScript), SQLAlchemy (Python), ActiveRecord (Ruby), Entity Framework (.NET), and Hibernate (Java).
Beyond developer ergonomics, ORMs eliminate entire categories of bugs. SQL injection is impossible because every parameter flows through typed binding. Type errors surface at compile time instead of runtime. Migrations get tracked in version control. The tradeoffs are a learning curve, occasional performance pitfalls (N+1 queries), and the need to escape to raw SQL for advanced queries.
How SheetLinkWP relates to ORM
The SheetLinkWP backend uses Prisma as its ORM on top of PostgreSQL. The WordPress plugin uses the WordPress standard $wpdb layer with prepared statements - not an ORM proper, but the same safety properties. Both paths rule out SQL injection by design, because raw string concatenation into SQL never happens.