Most people will be familiar with definition #1 of this word (from The Free Online Dictionary:):

a. A building or complex in which units of property, such as apartments, are owned by individuals and common parts of the property, such as the grounds and building structure, are owned jointly by the unit owners.

b. A unit in such a complex.

But in my studies of history, I have also come across another meaning, which is less known, but very useful conceptually. It is definition #2 of this word:

a. Joint sovereignty, especially joint rule of territory by two or more nations, or a plan to achieve it: “The allies would fear that they were pawns in a superpower condominium” New Republic.

b. A politically dependent territory.

Below is the passage from Tragedy & Hope: A History of the World in Our Time by Carroll Quigley, where I first encountered this word used this way.

“The extravagances of the Khedive Ismail (1863-1879), which had compelled the sale of his Suez Canal shares, led ultimately to the creation of an Anglo-French condominium to manage the Egyptian foreign debt and to the deposition of the khedive by his suzerain, the Sultan of Turkey. The condominium led to disputes and finally to open fighting between Egyptian nationalists and Anglo-French forces. When the French refused to join the British in a joint bombardment of Alexandria in 1882, the condominium was broken, and Britain reorganized the country in such a fashion that, while all public positions were held by Egyptians, a British army was in occupation, British “advisers” controlled all the chief governmental posts, and a British “resident,” Sir Evelyn Baring (known as Lord Cromer after 1892), controlled all finances and really ruled the country until 1907.”