By creating a histogram you're asking tableau to make "bins" of your profit value and show you the number of rows in your data that have a profit value within those bins. E.g. if the profit on a row was 300, that row would be counted in the 250-500 bin. The count of profit is a count of the number of rows data that have that profit value.
More information here:
Please refer to the below screenshot. Once you create the histogram using any metric, tableau automatic generates the bins in the dimension section. So I have selected a bar of $283 which has count of profit which is 1757.
So this means it has grouped all the rows which has a profit of less than and equal to 283 and greater than equal to 0. There are 1757 rows like that. Refer below screenshot for the same.
Let me know if that clears your doubt.
Thanks and Regards,