# Definition:Line/Endpoint

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## Definition

Each of the points at either end of a line segment is called an **endpoint** of that line segment.

Similarly, the point at which an infinite half-line terminates is called **the endpoint** of that line.

In the words of Euclid:

*The extremities of a line are points.*

(*The Elements*: Book $\text{I}$: Definition $3$)

## Also known as

The term **endpoint** can also be seen rendered as **end point**.

The more archaic term **extremity** can also be found, in particular in T.L. Heath's translation of *Euclid: The Thirteen Books of The Elements*.