Simple Definition:

The median is a statistical measure [a way to analyze and understand data] that represents the middle value in a dataset [a collection of information or numbers] when the values are arranged in ascending or descending order. For example, in the dataset {2, 4, 6, 8, 10}, the median is 6 because it is the middle value.

Very Simple Definition:

The median is the middle number in a group of numbers. For example, in the numbers 2, 4, 6, 8, 10, the median is 6 because it is in the middle.