In sailing and maritime history, quadrant primarily refers to a historical navigation instrument used to measure the altitude of celestial bodies to determine latitude. It is shaped like a quarter-circle (90 degrees), which is the source of its name. Here is a detailed breakdown of the term:

1. The Navigational Instrument (Mariner's Quadrant)
Purpose: Developed from the astrolabe, the quadrant was used in the 15th to 18th centuries to measure the altitude of celestial bodies (like Polaris or the sun) above the horizon to calculate a ship's latitude.

Description: It is a flat plate, typically made of brass or wood, spanning a 90-degree arc. It features two sights on one edge, a graduated scale on the curve, and a plumb line (string with a weight) hanging from the center.

How it Works: A navigator would sight a star (like Polaris) through the pinholes while allowing the plumb line to hang freely. The line would cross the graduated scale, indicating the angle of the star, which corresponds to the ship's latitude.

Variations:
Gunter Quadrant: A specialized 17th-century quadrant featuring graphs to find time, date, and sun position.

Davis Quadrant (Backstaff): A more advanced, safer version for measuring the sun without looking directly at it.

Superseded by: The quadrant was later replaced by the sextant, which provides higher accuracy.

2. The Steering Component (Steering Quadrant)
Description: A mechanical component used in a vessel's steering system. It is a curved yoke (shaped like a quadrant) attached to the rudder stock.

Function: It serves as a tiller, allowing steering cables, chains, or hydraulic systems to turn the rudder, translating the wheel movement into steering action.

3. Geographical/Weather Use
Definition: A quadrant can refer to a 90-degree sector of an area, often used in navigation or weather reporting, such as the "Northwest quadrant" of a storm.