noun
peeping Tom; voyeur
Refers to a person who secretly watches others, especially for sexual gratification. Often used in criminal or creepy contexts.
隣のアパートに覗き魔が出たらしい。
Apparently a peeping Tom has been spotted in the neighboring apartment building.
警察はその覗き魔を逮捕した。
The police arrested the voyeur.
覗く is the verb 'to peek' or 'to look in', while 覗き魔 is a noun for a person who habitually peeps, often with a negative connotation.
Compound of 覗き (のぞき, 'peeping', from 覗く) and 魔 (ま, 'demon' or 'fiend'), literally 'peeping fiend'.