order of the day

noun3

1. •
   The business to be done by a body (such as a legislature) on a particular day; an agenda.

   • The order of the day for the House to resolve into a Committee of the whole, to take into further consideration, the petition of Ezekiel Hart, Esquire, being read. — 1808
2. •
   (figurative) The most significant aspect of something; what is necessary or appropriate.

   • White tie and tails are the order of the day.
3. •
   The general directive of a commander-in-chief or the specific instructions of a commanding officer.