if they have SRT-4's they are the Mopar Performance Staged kits.
if its older TD's... there were MP stage 1 and 2 (dunno about 3.. didnt think they had one then) computers with more agressive programming.
if they are talking about turbo's specifically they "stage" is usually referring to the turbine wheel and housing combo. the larger the stage number (1,2,3,5 etc) the flowier the turbine but also the laggier the response is given a set engine displacement/headflow/etc. stage 1 is stock on a garrett turbo. the other stages also require a stock turbine housing to be machined to fit the different size wheel.