what is the distributor o ring, and rear main seal on 1995 Honda Civic

on estimate it says "Distributor cap leaking rear main seal. I couldn't find those parts in the description section

Asked by for the 1995 Honda Civic
The distributor o ring is described here
The rear main seal is at the rear of the engine , where the crankshaft couples to the transmission.
Incidentally a badly leaking distributor o ring can appear to be a leaking rear main seal since the distributor is located directly above the rear main seal.