The red and green arrows that you see on Top Lists screens, for example, on the Top files or Top pages, Top exit links?, etc, indicate a change in position over a given period of time.
So for example: you are looking at Top Pages for seven days back, and you see that the most visited page has:
a "1" in the first column, followed by a green arrow and a "(3)" in the second column.
This tells you that the most viewed page for the last seven days was the third most viewed page for the preceding period of seven days (i.e. 7-14 days back).
The ranking of the position has moved from 3 to 1.
The horizontal orange icon tells you that there has been no change in position.
The chart has been designed to resemble Billboard music charts, that show the popularity of songs through time.