Implicit -> When the detach procedure is initiated by the network(MME).
MME informs the UE with an EMM message (Service Reject/ TAU Reject) with EMM cause as "implicitly detached" only when the UE initiates any EMM procedure.
It then initiates the detach procedure by sending a DETACH REQUEST message to the UE
Detach type IE can either be "re-attach required" or "IMSI detach". For both of them there is a separate approach, i.e. how & why the bearer contexts are retained & how they are reestablished,etc.
Explicit -> When the UE initiates the detach procedure by sending a DETACH REQUEST message.
Again the detach type can be either ‘EPS detach’ / ‘IMSI detach’ / ‘Combined EPS/IMSI detach’.