Released in April 2011, Flash Professional CS5.5 was not a full version number jump (like CS6), but it was a significant update. It arrived at a time when the "Flash vs. HTML5" debate was reaching a fever pitch, and Apple had famously banned Flash from iOS devices.
Since "thethingy" isn't a standard technical term in Adobe Flash Professional CS5.5 ADOBE FLASH PROFESSIONAL CS5.5 -thethingy-