system call

noun2

1. •
   A function provided by an operating system to allow userspace programs access to privileged features, such as accessing the system's hardware.

   • The OS provides a system call to open a file, returning file descriptor that can be used to access it.
2. •
   A particular invocation of an operating-system-provided system-call function.

   • After a system call, control is returned to the process.