Implicit memory refers to a memory that a person does not know exists; a memory that is retrieved unconsciously; memory that is not deliberate or conscious, but exhibits evidence of prior experience.
Moreover, Implicit memory is demonstrated by means whereby conscious awareness is not always necessary, such as implicit priming, skill learning, and conditioning; memory not involving conscious recollection.
When we recollect something but are not consciously aware that we are trying to do so. (see Explicit memory)
Other /More definition:
implicit memory refers to the condition of memory in which a person cannot recall past events despite acting in response to them.