Requirements ontology offers a mechanism to map requirements for cloud computing services to cloud computing resources. Multiple stakeholders can capture and map knowledge in a flexible and efficient manner. The major contribution of the paper is the definition and development of an ontology for cloud computing requirements. The approach views each user requirement as a semantic intelligence task that maps and delivers it as cloud services. Requirements are modelled as tasks designed to meet specific requirements, problem domains that the requirements exist in, and problem-solving methods which are generic mechanisms to solve problems. A meta-ontology for cloud computing is developed and populated with ontology fragments on to which cloud computing requirements can be mapped. A critical analysis of the usage of ontologies in the requirements process is made and a case study is described that demonstrates the approach in a real-world application. The conclusion is that problem-solving ontologies provide a useful mechanism for the specification and reuse of requirements in the cloud computing environment.