An order was a command from a superior officer.
Picard was ordered to take command of the Enterprise by Admiral Satie (TNG: "All Good Things...")
Commander Data stated "By order of Starfleet, I hereby take command of this vessel" (TNG: "Redemption II")
Picard stated "the claim 'I was only following orders' has been used to justify too many tragedies in our history" (TNG: "Redemption II")
Picard was ordered to relinquish command of the Enterprise to Captain Jellico. (TNG: "Chain of Command, Part I")