In a monarchy, a queen is the female ruler of the country. Whether you are the Queen of England or the queen of a honey bee colony, you are the female in charge.
A queen inherits the title and the job, either from her father (the king) or her mother (the queen). Sometimes the term "queen consort" is used for a king's wife — in this case, the queen isn't the ruler, but merely married to the guy in charge. Many fairs, festivals, and other events crown an honorary queen, so you might be crowned the butter queen at the state fair. There's a queen in chess, the most powerful piece on the board, and a deck of cards has four queens. The most important bee in a colony is also a queen.