Histogram chart - What do the y-axis numbers mean?

["Marlon Nelson" <marlon nelson gmail com>]

I originally thought this was a bug and was about 30 seconds from
submitting one to bugzilla when I began to suspect the problem is with
my understanding of what a histogram is.

With the data listed below (frequency of daily returns of Merrill
Lynch stock over the last 10 years), I created a histogram chart.  The
highest point on the chart reaches 50,000.  I was expecting 1011.

Reading a bit from wikipedia, I see what I was actually expecting to
see is a bar chart.

But given a histogram chart of this data, what do the y-axis numbers mean?

Bin     Frequency
-15%    1
-13%    1
-11%    4
-9%     6
-7%     13
-5%     53
-3%     167
-1%     510
1%      1011
3%      489
5%      156
7%      57
9%      26
11%     6
13%     4
15%     3
17%     2

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