Umur was one of the Cardassian numbering systems. The Umur numbering base originated with the warrior caste in Cardassian society, and was later used by the Cardassian Union military.
In 2369, the Cardassians expressed interest in sending what they called an unarmed research vessel through the Bajoran wormhole into the Gamma Quadrant. When Chief of Operations Miles O'Brien of Deep Space 9 sent specifications for the impulse energy buffers to the Cardassians in order to prepare their ships for installation of the buffers, someone translated it into umur rather than the mercantile base damur.
As a result when the ship arrived at DS9 the clearance was too tight to permit the installation of the buffer. In a meeting to discuss the mistake and O'Brien's reaction to the problem, Odo pointed out that if the specifications were translated into damur that it would be closer to what O'Brien wanted. The mistake also tipped DS9 staff off that the ship was not the unarmed research vessel the Cardassians claimed it to be, but rather a military ship in disguise. (DS9 novel: Bloodletter)