1.
a line of latitude on the Earth's globe either 23º 26′ north of the equator or 23º 26′ south
2.
either of two circles on the celestial sphere that have the same latitudes and mark the limits of the apparent north-and-south movement of the Sun.
3.
the hottest part of the Earth, between the Tropic of Cancer and the Tropic of Capricorn