What is the value that falls in the middle position when the data is arranged in order from smallest to largest?

That's the median. (It is also the 50th percentile.) Exactly half the data lie above the median and half lie below it.

For example, consider the following list of numbers: 4, 2, 6, 7, 3, 8, 9.

Arranging the numbers from least to greatest, we get: 2, 3, 4, 6, 7, 8, 9.

The number 6 is in the middle, so 6 is the median of the data set. If the number of data points is even and no one number is in the center, you must find the average of the two data points in the middle of the list to determine the median.