In their daily practice, most enterprises collect, store, and manage personal information for customers in order to deliver their services. In such a setting, privacy has emerged as a key concern as companies often neglect or even misuse personal data. In response to this, governments around the world have enacted laws and regulations for privacy protection. These laws dictate privacy requirements for any system that acquires and manages personal data. Unfortunately, these requirements are often incomplete and/or inaccurate as many RE practitioners might be unsure of what exactly are privacy requirements and how are they different from other requirements, such as security. To tackle this problem, we developed a comprehensive ontology for privacy requirements. To make it comprehensive, we base our ontology on a systematic review of the literature on privacy requirements. The contributions of this work include the derivation of an ontology from a previously conducted systematic literature review, an implementation using an ontology definition tool (Protégé), a demonstration of its coverage through an extensive example on Ambient Assisted Living, and a validation through a competence questionnaire answered by lexical semantics experts as well as privacy and security researchers.