What is Raw expressions in Laravel, and what role does it play in a real application?

What is Raw expressions in Laravel, and what role does it play in a real application? In Laravel, raw expressions should be understood as part of a larger application architecture rather than as an isolated API call. Raw SQL expressions can be used for cases the fluent API cannot conveniently express, but user input must never be concatenated into raw SQL. A strong understanding includes its purpose, the layer where it belongs, the data or request flow it affects, and the situations where another mechanism may be more appropriate. Practical context: Laravel Query Builder provides a fluent interface for constructing SQL queries for common filtering, joining, grouping, aggregation and data modification operations. The specific focus here is raw expressions: Raw SQL expressions can be used for cases the fluent API cannot conveniently express, but user input must never be concatenated into raw SQL. This question is designed to test not only terminology, but also how the concept fits into Laravel's request, application, database, security, or deployment workflow.