What is SQL Server internal query execution context (task, worker, request) relationship?

A request is a query execution unit, a task represents work to be done, and a worker is the OS thread executing it.

SQL Server execution is layered. A request is the logical query submitted by a session. Each request is broken into one or more tasks depending on parallelism and operator execution. Workers are SQLOS-managed threads bound to schedulers. Workers execute tasks cooperatively, yielding when waiting for resources. This architecture decouples logical query execution from physical thread execution, enabling fine-grained scheduling, parallelism, and resource governance.