What is a "cross check"? Shortly before take-off, and again before landing, the cockpit (no way to tell whether it was the Captain or First Officer) came on over the speakers, stating:


  Flight Attendant's, prepare for take-off/landing and cross-check


What is a cross-check?
This website has the definition:


  Crosscheck is a generic term used by pilots and flight attendants
  meaning that one person has verified the task of another. In the
  cabin, flight attendants crosscheck one another’s stations to make
  sure the doors are armed or disarmed as necessary.