What is "zmanim"

Zmanim (, literally "times", singular zman) are the specific times of the day with applications in Jewish law.

• In Jewish law, a calendar day is defined as running from "evening" to "evening." This is based on the repetition of the phrase "... and there was evening, and there was morning ..."—evening preceding morning—in the account of creation in Genesis.
• Additionally, Jewish law requires certain activities to be undertaken "during the day"—or at a certain time during the day—while other activities are to be undertaken "at night"—or at a certain time during the night.

For either purpose, the status of the twilight hours just after sunset or just before sunrise is ambiguous. Judaism provides its own definitions for this period; at the same time, various rabbinic authorities differ on just how those definitions are to be applied for different purposes.