The active unoptimized is the path to the LUN which is not owned by the storage processor. This situation occurs on Arrays which are Asymmetric Active-Active, for example: HP EVAs. ESX from version 4 onwards is ALUA aware thus differentiating between optimized and unoptimized paths.
Optimized paths: are the paths to the Storage Processor which owns the LUN.
Unoptimized paths: are the paths to the Storage Processor which does not own the LUN. And has a connection to the LUN via interconnect between the processors.
There is lot of detailed documentation on this topic on the web, for example:
http://www.yellow-bricks.com/2009/09/29/whats-that-alua-exactly/
http://frankdenneman.nl/storage/esx4-alua-and-hp-continuous-access/
..hth!