A Queen Consort is a woman who earns the title of queen because she is married to a king. She typically has no official political power, and she may not legally hold the throne in many nations after her husband's death, although she may act as regent to care for the kingdom until her children grow up. The male counterpart of a Queen Consort is a King Consort.
Typically, a Queen Consort is of royal blood, but she is not entitled to rule her country by birthright like her husband, the King Regnant. In the case of a King Consort, the Queen rules the country by right. In both cases, the title is given as a courtesy, recognizing the important role of the Queen or King Consort in the life of the monarch. The Queen Consort is also typically entitled to the same titles as her husband, and she must be treated with the same gravity and respect to which her husband is accustomed.
In addition to Queens Consort, it is also possible to find Princesses Consort and Empresses Consort, along with Princes Consort and so forth. As a general rule, when someone marries a King, the King and his advisers confer the title of Consort upon her. However, in some cases she may be given a different title, for political or social reasons. For example, it is rumored that Camilla Parker-Bowles, the Duchess of Cornwall, will be known as Princess Consort when her husband takes the throne of England.
Although a Queen Consort does not officially have political power, she is often a very powerful and prominent social figure. Many Kings take advice from their Consorts and consider their input into the running of the nation, so although the woman is not officially the monarch, she does in some sense act as one.
The Queen Consort is also an important public figure for the monarchy. She participates in social events, sponsors charities, and engages in various social and political issues in her nation, and often becomes a prominent and well-loved figure. Many have famously supported specific causes, ranging from children's welfare to votes for women. She is also, of course, the mother of the heirs to the throne.
In rare cases, Kings and Queens have ruled their nations and holdings equally, with neither partner being considered a consort. In general, this has occurred when a King Regnant and a Queen Regnant marry, uniting two empires.