  The \emph{arbelos} is the shape bounded by three mutually tangent semicircles
with collinear diameters. Recently, Sondow introduced the parabolic analog, the
\emph{parbelos} and proved several properties of the parbelos similar to
properties of the arbelos. In this paper we give one step further and
generalize the situation considering the figure bounded by (quite) arbitrary
similar curves, the \emph{$f$-belos}. We prove analog properties to those of
the arbelos and parbelos and, moreover, we characterize the parbelos and the
arbelos as the $f$-beloses satisfying certain conditions.
