(arithmetic) A vulgar fraction in which the magnitude of the numerator is less than or equal to that of the denominator, such as 2/3.

plural of proper fraction

(astronomy) The change in apparent position of a celestial body due to that body's velocity relative to the Sun.

plural of proper adjective

(physics) The acceleration felt by an object, as opposed to the coordinate acceleration. For example the acceleration of an object at the surface of the Earth is 9.81 m/s² upwards, but has no coordinate acceleration. The proper acceleration of an object is Lorentz invariant.

plural of proper name

(rare) The quality of being a proper noun.

plural of proper class

(set theory) A class which is not a set.

(dated, linear algebra) An eigenvalue.