Which of the following best describes a programming language?

A programming language is fundamentally defined as a system of conventions and symbols for writing code. It serves as a medium through which humans can communicate instructions to a computer, enabling the creation of software applications, algorithms, and control structures. Programming languages are composed of syntax and semantics that dictate how the code should be structured and interpreted by the computer.

This choice accurately embodies the essential function of a programming language, which is to provide a structured way to write code that can be compiled or interpreted into actions performed by the computer. Other options, while related to computing, do not capture this core function of programming languages. Computer hardware refers to the physical components of a computer system, storing data pertains to data management, and visual representations of data structures focus on how data is organized rather than the process of writing code itself.