What's the context? In Europe, you can log PICUS (PIC Under Supervision). My understanding is that this is basically where the FO logs his legs as PICUS and has the Captain sign his logbook.
I'm guessing the context is the number of FAA certificates and ratings that allow the counting of certain times one is performing the duties of PIC while under the supervision of a "real" PIC.
If that's what the OP is talking about, it's been in the regs in various forms but the October 2009 Part 61 revision added more about when it can be logged as PIC time:
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61.51(e) Logging pilot-in-command flight time. (1) A sport, recreational, private, commercial, or airline transport pilot may log pilot in command flight time for flights-
(iv) When the pilot performs the duties of pilot in command while under the supervision of a qualified pilot in command provided—
(A) The pilot performing the duties of pilot in command holds a commercial or airline transport pilot certificate and aircraft rating that is appropriate to the category and class of aircraft being flown, if a class rating is appropriate;
(B) The pilot performing the duties of pilot in command is undergoing an approved pilot in command training program that includes ground and flight training on the following areas of operation—
( 1 ) Preflight preparation;
( 2 ) Preflight procedures;
( 3 ) Takeoff and departure;
( 4 ) In-flight maneuvers;
( 5 ) Instrument procedures;
( 6 ) Landings and approaches to landings;
( 7 ) Normal and abnormal procedures;
( 8 ) Emergency procedures; and
( 9 ) Postflight procedures;
(C) The supervising pilot in command holds—
( 1 ) A commercial pilot certificate and flight instructor certificate, and aircraft rating that is appropriate to the category, class, and type of aircraft being flown, if a class or type rating is required; or
( 2 ) An airline transport pilot certificate and aircraft rating that is appropriate to the category, class, and type of aircraft being flown, if a class or type rating is required; and
(D) The supervising pilot in command logs the pilot in command training in the pilot's logbook, certifies the pilot in command training in the pilot's logbook and attests to that certification with his or her signature, and flight instructor certificate number.
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