What is the definition of a line?

Answer 1

There are many definitions, here is one:

A line (straight line) is a geometrical form that is straight, infinitely long and infinitely thin, consisting of an infinite number of finite points. Any two points can be connected to form a line. (A straight line is the shortest path between any two points.)

A geometric line can also be curved, and may form a closed path.

A line of poetry is just that : the words in a single line, which are defined by meter and by rhythm, and possibly by characteristics such as assonance, consonance, and rhyme.

A line in practical uses can be a string used for fishing, a rope used to do work, or a boundary or borderline. It can be a number of objects or constructs in a row.