1 (one, unit, unity) is a
number representing a single or the only
entity. 1 is also a
numerical digit and represents a single
unit of
counting or
measurement
Measurement is the quantification of attributes of an object or event, which can be used to compare with other objects or events.
In other words, measurement is a process of determining how large or small a physical quantity is as compared ...
. For example, a
line segment
In geometry, a line segment is a part of a straight line that is bounded by two distinct end points, and contains every point on the line that is between its endpoints. The length of a line segment is given by the Euclidean distance between ...
of ''unit length'' is a line segment of
length
Length is a measure of distance. In the International System of Quantities, length is a quantity with dimension distance. In most systems of measurement a base unit for length is chosen, from which all other units are derived. In the Interna ...
1. In conventions of sign where zero is considered neither positive nor negative, 1 is the first and smallest
positive integer
In mathematics, the natural numbers are those numbers used for counting (as in "there are ''six'' coins on the table") and ordering (as in "this is the ''third'' largest city in the country").
Numbers used for counting are called ''cardinal n ...
.
It is also sometimes considered the first of the
infinite sequence of
natural numbers, followed by
2, although by other definitions 1 is the second natural number, following
0.
The fundamental mathematical property of 1 is to be a