ネコババ means keeping something one found instead of returning it. It can also mean concealing one’s wrongdoing.
Usage Notes
It is often used when one finds a dropped item and keeps it for themselves, rather than turning it in to the police or a lost-and-found center on the premises.
ネコババ is a noun. When used as a verb, it becomes ネコババする.
After Meimi makes her first appearance as a magical thief, her nun-in-training classmate Seira suggests the name Saint Tail. She adds that they can use the sealed confessional as a meeting room.
芽美:
「ちょっと それってざんげ室(ネコババするんじゃ……!!」
“Hold up, isn't that misappropriating the confessional?”