In this paper, I answer the question of what time is. First, however, I consider why one might ask this question and what exactly it is asking. The latter consideration reveals that in order to answer the question, one must first engage in a more basic investigation of what a thing, anything at all, is. Such radical investigation requires a special methodology. After briefly characterizing this methodology, I show how it can be employed to answer the titular question. This answer (...) is significant not merely because it illuminates something of perennial interest, but because it is essential to a comprehensive and fully satisfactory metaphysics of time and, hence, to a view of the full structure in reality. (shrink)