Many if not most airlines encourage Captains to let First Officers gain experience by "role reversal". There are many versions of this but in general it involves the F/O doing the majority of the duties normally assigned to the Captain and vice versa. This would include the tasks involved in conducting the approach.
Such role reversal may involve the F/O doing not only the aircraft handling including takeoffs and landings but also other tasks normally assigned to the Captain, e.g. flight planning, load sheet and technical log inspection, passenger liaison and PA etc., even though the Captain retains the legal responsibility as aircraft commander. In this case the F/O is acting as if he/she were the Captain until the Commander decides other wise, i.e. the F/O is temporarily "in charge" and the Captain is (temporarily) the co-pilot.
This may be characterised as "Pilot in Charge Command (or in Charge) Under Supervision" flying, with the acronym PICUS, and is valid for recording experience for crew licencing purposes.
"PicMA" stands for Pilot in charge Monitored Approach, since during the approach on such a sector the F/O will be doing the captain's normal duties as pilot responsible for the overall conduct or "in charge" of the flight, and hence doing the monitoring during the approach. The Captain as Aircraft Commander of course remains legally responsible for supervising the actions of the copilot, whatever degree of role reversal is being undertaken.
Depending on specific company and national regulations and processes this may have different local and legal definitions, e.g. "pilot in command under supervision", "leg and leg flying", "first officer flying", "co-pilot sector", "role reversal", etc. Professional pilots understand what is meant in the current context and the term "pilot in charge" is used here to convey that the "monitored approach procedure" is part of the duties to be transferred during sectors where the Captain allows the other pilot to carry out the takeoff and landing. These issues are discussed in some detail in the section on First Officer Flying.