1. Contact List: The most common meaning refers to a personal address book containing names and contact information (phone numbers, addresses, etc.) of people the owner considers important or useful. This can include friends, family, business contacts, potential romantic partners, etc.
2. Secret List of Lovers/Contacts: This meaning is more salacious and implies a list of romantic or sexual contacts - often kept secret. It often evokes a sense of intrigue and suggests a person with a network of potential partners.
3. Any Small Notebook: While less common, "little black book" can also refer to any small, black notebook used for various purposes, like keeping notes, writing down ideas, or tracking tasks.
The exact meaning of "little black book" depends on the context. If you hear someone talking about their "little black book," pay attention to other clues in the conversation to understand their intended meaning.