Uncached lookup: The informatica server doesnot build a 
cache for temporary starage of data. Wenever it need to 
refer to the look up table, it scans the source directly.

Dynamic Cache: The informaatica server builds a cache of 
the source wen the workflow runs for the first time and it 
updates the cache records dynamically after each row it 
loads to the target. Means, if a target row gets updated, 
the dynamic cache also gets updated automatically after 
that particular row comitted in the target.

or 
Dynamic cache - can be configured as connected lookup only. 
It does not support lookup on flat file. Can have only 
equality operator in lookup condition.

Static cache - can be configured as connected as well as 
unconnected lookup. Supports lookup on flatfile. Can have 
any relational operator in lookup condition.