The programming language widely used for system-level programming is C. This language is favored for its efficiency, control over system resources, and close-to-hardware capabilities. C allows developers to write programs that can manipulate hardware directly, which is essential for operating system development, embedded systems, and various applications requiring high performance. Its portability enables code written in C to run on different hardware architectures with minimal modifications. Moreover, C's syntax has influenced many other programming languages, solidifying its importance in the field of software development and system architecture.