Which term describes a special relationship where each input corresponds to one output?

The term that describes a special relationship where each input corresponds to one output is "function." In mathematical terms, a function takes an input, processes it through a specific rule or relationship, and produces exactly one output. This concept is central to many areas of mathematics and helps in modeling various real-world situations.

For instance, if you have a function that defines how to compute the area of a rectangle based on its length and width, each pair of inputs (length and width) will yield one specific output (the area). This unique pairing of inputs to outputs exemplifies what makes a function distinct.

The other choices represent different concepts. An equation is a statement that two expressions are equal, but it does not specifically indicate a one-to-one relationship like a function does. An algorithm refers to a step-by-step procedure for solving a problem but is not confined to the input-output relationship that defines a function. A sequence, meanwhile, is a list of numbers arranged in a specific order, which can have multiple outputs for certain inputs and does not adhere to the strict input-output mapping of a function. Understanding these definitions helps clarify why "function" is the most accurate term in this context.