Final answer:
The question about Guru Nanak's key terms for divine revelation is incomplete, lacking specific terms. Therefore, a detailed answer is not possible without further information. However, Guru Nanak's teachings on one universal God and moral living are central to Sikhism.
Step-by-step explanation:
The student has asked to identify and explain the three key terms that Guru Nanak employed to describe the nature of divine revelation. Unfortunately, the question appears to be incomplete as it does not provide the specific terms used by Guru Nanak for this explanation.
Without these specific terms, it is not possible to provide a detailed answer. However, Sikhism, as founded by Guru Nanak, emphasizes the worship of one universal God, the equality of all human beings, and the importance of leading a moral and disciplined life for spiritual development. It would be important to reference Guru Granth Sahib, the holy scripture of Sikhism, which contains the teachings of the Sikh Gurus, to find specific terms and concepts relevant to divine revelation in Sikhism.