Which concept pertains to functions that are defined by different expressions depending on the interval?

Piecewise functions are defined by different expressions depending on the interval in which the input variable falls. This means that for different segments of their domain, these functions can follow different rules or formulas. Such a structure allows for greater flexibility in modeling real-world situations where conditions change; for example, a tax function might increase rates past certain income thresholds, or a physical system might behave differently under varied conditions.

This characteristic of having distinct rules for different portions of the domain distinguishes piecewise functions from continuous functions, which must not have any breaks or jumps and are defined everywhere in their domain with a single continuous expression. Linear functions represent straight lines and have a constant rate of change, while monotonic functions are those that are either entirely non-increasing or non-decreasing across their entire domain. These concepts do not exhibit the segmented nature crucial to defining piecewise functions.