Pramana (Tib. tsema) is a sanskrit term which refers to different notions. Its prime meaning, and its translation in this case, is 'valid cognition', a correct knowledge of a particular object. Valid cognition can either be direct perception or inference.
As a consequence, the term is used to refer to the corpus of Buddhist teachings on epistemology (the science of cognition, i.e. how do we know things) and ontology (which investigates the nature of existence), as those two aspects are inextricably linked in Buddhism. The forefathers of those teachings are the Indian masters Dignaga and Dharmakirti. They are taught in all shedras since they are the basis for debate, an important learning tool in traditional monastic universities. In this context the term is sometimes translated as Buddhist logic.