A more thorough explanation:

Definition: The state or quality of being concealed, especially from those who would be affected by the concealment; hidden.

Examples:

• Keeping a surprise party a secret from the person it is being thrown for.
• A government agency keeping classified information hidden from the public.
• A company keeping their new product design a secret from their competitors.

The examples illustrate secrecy because in each situation, information is being intentionally kept hidden from certain individuals or groups. In the case of the surprise party, the information is being kept hidden from the person it is being thrown for in order to maintain the surprise. In the case of the government agency, the information is being kept hidden from the public in order to protect national security. In the case of the company, the information is being kept hidden from competitors in order to maintain a competitive advantage.