A hyperbola is the locus of a point P such that the absolute difference of its distances from two fixed points (foci F1 and F2) is constant: |PF1 - PF2| = 2a. The standard equation is $x^2$/$a^2$ - $y^2$/$b^2$ = 1 with transverse axis along the x-axis. Here a is the semi-transverse axis and b is the semi-conjugate axis. The relation $c^2$ = $a^2$ + $b^2$ holds (contrast with ellipse where $c^2$ = $a^2$ - $b^2$). The eccentricity e = $\frac{c}{a}$ > 1 always. Note that unlike the ellipse, a need not be greater than b.