IN MATH: 1. n. a way of testing a graphed function to determine if it is 1to1, uses each yvalue at most once, has the possiblility of having an inverse function. EX. The graph of y=x² fails the horizontal line test because one or more horizontal lines pass through the curve simultaneously. The line through (2,4) and (2,4), for example.

IN ENGLISH: 1. as defined above.
APPLICATION: See list 300.
www.mathnstuff.com/math/spoken/here/1words/h/h7a.htm 