noun
parting gift; souvenir left behind; aftereffect
Literally 'a souvenir left behind'. Can refer to a physical gift left for someone, or figuratively to a lasting effect or memory left by a person or event. The figurative use is less common.
彼は旅立つ前に、家族に置き土産を残した。
Before leaving on his journey, he left a parting gift for his family.
その政治家の汚職事件は、政界
The politician's corruption scandal became a lasting aftereffect in the political world.
土産 is a general souvenir or gift brought back from a trip, while 置き土産 specifically implies leaving something behind for someone else, often with a sense of finality.
忘れ形見 is a keepsake or memento left by a deceased person, carrying a stronger emotional and memorial nuance than 置き土産, which can be used more broadly for any parting gift or aftereffect.
Compound of 置き (oki, 'leaving, placing') + 土産 (miyage, 'souvenir, gift'). The literal meaning is 'a souvenir left behind'.