Euclid's postulates are a set of five foundational principles that form the basis of Euclidean geometry. They were introduced by the ancient Greek mathematician Euclid in his work, "Elements." These postulates describe the properties of points, lines, and planes, establishing rules for constructing geometric figures. The first postulate states that a straight line can be drawn between any two points. The second postulate asserts that a finite straight line can be extended indefinitely. The third postulate allows for the creation of a circle with any center and radius. The fourth postulate states that all right angles are equal, while the fifth postulate, known as the parallel postulate, addresses the uniqueness of parallel lines.