What is the best description for the lines

Lines are described as connecting curve joining two points.

Step-by-step explanation:

In coordinate geometry, graph theory, we have points which do not occupy any space.

Any two points can be connected by a curve or a straight line.  If two points are joined by a straight line, then we have the slope of the line i.e. the tangent of angle of the line with x axis is constant.

Straight lines would be of the form ax+by+c=0

Hence in equation form, lines would have equations in linear form of both x and y.

Lines have constant slope throughout the region.

Lines can be extended from -infinity to +infinity

Any two distinct  points can make a line, but 3 points need not lie on the same line.

the graph on the bottom right