One-dimensional refers to a geometric concept that describes an object or space that has only one measurable extent: length. In a one-dimensional space, such as a straight line, there are no other dimensions like width or height. This means that any point on the line can be defined by a single coordinate. In mathematics, one-dimensional objects can be represented using a number line, where each point corresponds to a real number. Examples of one-dimensional entities include line segments and curves that can be traced without lifting a pencil, as they only require one measurement to describe their position.