Frames per second. Notice the X in the write column for 720P 59.94 12 bit RGB 4:4:4 (left side table). Now look at the 12 BIT RGB 4:4:4 section of the table on the right side. HD 720 is listed at 59. 59 is less than 59.94 which is why the left hand table contains an X.
You can match up all the X in the left hand table to speeds that are less than the frame rate in the right hand table. It's the same data in a different form.
Just an observation, would it not make more sense for the table on the right to indicate with red numbers the fail value of that field, in other words right at the bottom, the 2K is 17 and 38 in green, is this a passing value or a failing value? If I can see that 17 is too low then have in brackets the lowest "passing value" for example 17[red] 50[pass] for both read and right values?
The 17 and 38 in your example are neither Passing or Failing values. They are the determined Read and Write values according to Blackmagicdesign's speed test application. The chart on the left is the useful portion which tells you which formats your system can efficiently read and write based on those results. The X indicates that a particular format requires faster speeds than the results for optimum editing.
Yes. That measurement is Frames per Second. There is a complete instruction guide that identifies what each area of the test is and you can find that under the help menu of the Speed Test application. It is a very detailed pdf document.