a line that a curve approaches; the distance between the curve and an asymptote approaches zero
a horizontal line that a curve approaches from above or below; the curve tends towards a constant value, and its distance to the horizontal line tends towards zero
also called slant asymptotes, a line that a curve approaches as x tends towards ± inifinity; it can be defined by y=mx+b, where m≠0
a vertical line that a curve approaches from the left or right; the curve tends towards positive or negative infinity, and its distance to the vertical line tends towards zero