A sequence or function is considered "non-decreasing" if its values do not decrease as you move from one point to the next. This means that each value is either greater than or equal to the one before it. For example, in the sequence 1, 2, 2, 3, 4, the numbers do not drop at any point. Non-decreasing sequences are important in various fields, including mathematics and computer science. They are often used in algorithms and data analysis to ensure that data is organized in a way that allows for easier interpretation and processing.