Involuntary memory, as defined by Wikipedia, Involuntary Memory
The most famous literary example is from Marcel Proust, Remembrance of Things Past.
[Proust] describes an incident where he was eating tea soaked cake,
and a childhood memory of eating tea soaked cake with his aunt was
"revealed" to him. From this memory, he then proceeded to be reminded
of the childhood home he was in, and even the town itself.
This is the incident of the madeleine.
A technical definition of involuntary memory, from the first source, above, is:
Involuntary memory, also known as involuntary explicit memory,
involuntary conscious memory, involuntary aware memory, and most
commonly, involuntary autobiographical memory, is a subcomponent of
memory that occurs when cues encountered in everyday life evoke
recollections of the past without conscious effort. Voluntary memory,
its binary opposite, is characterized by a deliberate effort to recall