A production cel was used in the production of the show.  Handpainted with  xeroxed lines.

A sericel is.... (taken straight from Aimee's Cel Forum.   please don't kill me Aimee).....
not a real production cel, its basically a traced redone version of either original "sanctioned" 
artwork from that company, or its a newly traced version of what would have been a 
production cel.   There are usually limited editions of these (ie they are not one of a kind 
like production cels are)
Sericels are made using serigraphy (a xerox like process, but is more of an artform, with 
lots of inks. the more inks used the higher quality the sericel.)

You don't see many anime sericels.  I dunno know if the Eva cels are sericels or not.  Not 
referring to the printed ones that look like they have a background.  Those look like they 
were screen printed. 

and I have no idea what a regular cel is.  Unless you are referring to when someone 
says a cel is regular size.  Generally around 9" x 10 1/2"

Hope that helps.

Ja ne,

Kelly   ^_^   by no means an expert