The notation "X_n" typically represents a sequence of elements indexed by the natural numbers, where "n" indicates the position in the sequence. For example, in a sequence of numbers, "X_1" might be the first number, "X_2" the second, and so on. This notation is commonly used in mathematics, particularly in areas like calculus and statistics, to describe patterns or behaviors of sequences. In many contexts, "X_n" can also refer to random variables in probability theory, where each "X_n" represents a different outcome in a series of experiments. This allows for the analysis of trends and distributions over time, making it a crucial concept in fields such as data science and machine learning.