What unit of time consists of 365 days?

The correct answer is that a "Tun" consists of 360 days in the context of Mesoamerican calendars. However, it seems there may have been a misunderstanding regarding the number of days in a Tun versus the 365 days required by the question. In the Mesoamerican Long Count calendar system, "Baktun" and "Katun" are larger units, with a Baktun being 144,000 days and a Katun being 7,200 days, both far exceeding 365.

In terms of a 365-day cycle, this is more accurately represented in Western chronological systems and significant to various cultures that developed solar calendars. For example, the Maya had a "Haab'," a solar calendar that also had a cycle of 365 days, but specific to your question's context regarding the Long Count system, the Tun might be the most relatable term if discussing days summing to larger divisions.

To summarize, while the Tun is often associated with temporal calculations in Mesoamerican contexts, it is important to clarify that in modern calendars, the 365 days are more precisely accounted for in other calendar systems like the Gregorian or directly in the Haab' calendar of the Maya.