Jack Out: The process by which a Runner voluntarily ends his own run.
Jacking out is the act of the Runner choosing to end his/her run before it is completed. Jacking out immediately ends the run unsuccessfully, but it allows the Runner to avoid facing any ice s/he has not yet encountered and accessing what s/he may think is an ambush. The Runner has the chance to jack out during any approach except for when approaching the first ice protecting the attacked server.
The rules state that "The Runner cannot jack out while approaching the first piece of ice during a run." Can the Runner jack out after the subroutine on Cell Portal resolves and he is approaching the outermost piece of ice protecting the server?
Yes. "The first piece of ice" refers to the first time a piece of ice is approached during a run, and not the ice itself. The Runner approaches the ice and has the opportunity to jack out.