It describes something that is characteristic of a queen, such as:
* Queenly grace: elegant and dignified
* Queenly demeanor: regal and commanding
* Queenly attire: fit for a queen, usually lavish and ornate
Other related adjectives include:
* Regal: fit for a king or queen
* Royal: belonging to a king or queen
* Sovereign: having supreme power or authority
* Majestic: impressive and dignified