What does the term "fundamental" refer to?

The term "fundamental" refers to something that is basic or essential, serving as a foundation for further ideas or developments. It implies that it is a core concept that is crucial for understanding more complex ideas or systems. For instance, in mathematics, fundamental principles such as addition and subtraction are essential for grasping more advanced concepts such as algebra or calculus. Understanding what is fundamental allows individuals to build upon that knowledge effectively in various fields. Therefore, the option that aligns with this definition is correct.