a line by which a local or indeterminate problem is solved. A locus is a line, any point of which may equally solve an indeterminate problem. Thus, if a right line suffice for the construction of the equation, it is called locus ad rectum; if a circle, locus ad circumflexum; if a parabola, locus ad parabolam; if an ellipse, locus ad ellipsis; and so of the rest of the conic sections.