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.