X_4 is a term that can refer to various concepts depending on the context. In mathematics, it may denote a specific variable or element in a sequence or equation. In technology, it could represent a model or version of a product, such as a software application or hardware device. In the field of science, X_4 might be used to identify a particular compound or element in a chemical formula. Understanding the context in which X_4 is used is essential for grasping its specific meaning and implications in different disciplines, such as mathematics, technology, or science.