In analytic geometry, an asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity. For curves given by the graph of a function y = ƒ(x), there are potentially three kinds of asymptotes: horizontal, vertical and oblique asymptotes. Horizontal asymptotes are horizontal lines that the graph of the function approaches as x tends to +∞ or −∞.