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In analytic geometry, using the common convention that the horizontal axis represents a variable and the vertical axis represents a variable , a **-intercept** or **vertical intercept** is a point where the graph of a function or relation intersects the -axis of the coordinate system.^{[1]} As such, these points satisfy .

If the curve in question is given as the -coordinate of the -intercept is found by calculating . Functions which are undefined at have no -intercept.

If the function is linear and is expressed in slope-intercept form as , the constant term is the -coordinate of the -intercept.^{[2]}

Some 2-dimensional mathematical relationships such as circles, ellipses, and hyperbolas can have more than one -intercept. Because functions associate -values to no more than one -value as part of their definition, they can have at most one -intercept.

Analogously, an -intercept is a point where the graph of a function or relation intersects with the -axis. As such, these points satisfy . The zeros, or roots, of such a function or relation are the -coordinates of these -intercepts.^{[3]}

Functions of the form have at most one -intercept, but may contain multiple -intercepts. The -intercepts of functions, if any exist, are often more difficult to locate than the -intercept, as finding the -intercept involves simply evaluating the function at .

The notion may be extended for 3-dimensional space and higher dimensions, as well as for other coordinate axes, possibly with other names. For example, one may speak of the -intercept of the current–voltage characteristic of, say, a diode. (In electrical engineering, is the symbol used for electric current.)