a line which is not straight is called
Line (geometry) When geometry was first formalised by Euclid in the Elements, he defined a general line (straight or curved) to be "breadthless length" with a straight line being a line "which lies evenly with the points on itself".[5] These definitions serve little purpose since they use terms which are not, themselves, defined. In fact, Euclid did not use these definitions in this work and probably included them just to make it clear to the reader what was being discussed. In modern geometry, a line is simply taken as an undefined object with properties given by axioms,[6] but is sometimes defined as a set of points obeying a linear relationship when some other fundamental concept is left undefined.
Linear motion Linear motion (also called rectilinear motion[1]) is a one-dimensional motion along a straight line, and can therefore be described mathematically using only one spatial dimension. The linear motion can be of two types: uniform linear motion with constant velocity or zero acceleration; non uniform linear motion with variable velocity or non-zero acceleration. The motion of a particle (a point-like object) along a line can be described by its position   x  {\displaystyle x} , which varies with   t  {\displaystyle t}  (time). An example of linear motion is an athlete running 100m along a straight track.[2]