What and where is the opti-spark?

What is the thing mounted on top of the intake plenum on the upstream side of the air cleaner?

 

The opti-spark is the distributor, plus an optical section to monitor cam position. It's located on the front of the engine, bolted to the timing chain cover (just below the waterpump).

 

Optispark n. - (1) It's the bain of existence for some Corvette, F-body, and 9C1/Impala SS owners (2) Directly camshaft driven, optically triggered distributor stuffed convienently behind the water pump but in front of the timing cover on an LT1/LT4 engine (3) See http://shbox.com/1/component_location_views.html for more information

 

That is a funny question.

Anyways, what direction is "upstream"?