Digest of terms
experience of knowledge coming to an individual in some sense 'from beyond', and in its prime religious usage, from God. In particular Judaism, Christianity and Islam all see themselves as being religions of revelation, with prophets in miraculous receipt of personal disclosures from God, what theologians call revealed knowledge, which is contrasted with natural knowledge, the latter being discoverable by reason, the former depending on a supernatural source. The scriptures of these religions are regarded either as being, or as containing, revelation - which traditionally was contrasted too with 'inspiration', although for many liberal believers today that distinction has become rather blurred. (Hindu scriptures - different ones depending on the school of thought, but always including the core Veda texts - are also described in English as revelation, but while this accurately conveys the sense of their authority, it is also potentially misleading, since the Sanskrit term shruti, 'heard', is vague and in the context of Hindu thought implies neither communication from God nor mere personal insight.)
Alongside this specific usage, revelation may be used more analogically or symbolically as 'the light dawning' or 'a flash of inspiration' with its source not calculatingly controlled. The context for this might be one of scientific discovery (a so-called Eureka moment) or of moral insight. It might also refer to the kind of experience attributed to the Buddha at the time of his discovery of the path to enlightenment, an experience not regarded as having been the effect of any kind of personal disclosure 'from beyond' such as claimed, for example, by Muhammad, but the product of ascetic meditative preparation - from meditational depths within.
Revelation in the strict sense was often said to occur through the medium of dreams or voices, media nowadays viewed with considerable skepticism: as Hobbes famously commented, to say that God spoke to one in a dream is to say that one dreamed that God spoke to one. (Hence, in good measure, the above-mentioned tendency to merge revelation with inspiration.)
The challenge for anyone involved in making moral judgements is how to interpret and apply revelatory insights of any kind in the present moment.