A distinguishing feature of a person or thing.
For a given field or ring, a natural number that is either the smallest positive number n such that n instances of the multiplicative identity (1) summed together yield the additive identity (0) or, if no such number exists, the number 0.
The integer part of a logarithm.
The distinguishing features of a navigational light on a lighthouse etc by which it can be identified (colour, pattern of flashes etc.).
Being a distinguishing feature of a person or thing.
The quality of being eccentric or odd; any eccentric behaviour.
The ratio, constant for any particular conic section, of the distance of a point from the focus to its distance from the directrix.
The eccentricity of the conic section (usually an ellipse) defined by the orbit of a given object around a reference object (such as that of a planet around the sun).