A fuse resistor is an ordinary resistor (or a special fusible resistor, as Mike mentioned above) that is used as a fuse when its electrical characteristics are violated, resulting to its destruction --thus breaking the circuit.
In order to protect a portion of a circuit against over-current of, say, 100mA, I will simply insert a suitable resistor in he current path, according to the formula below:
P = I^2*R = U^2/R <=>
R = P/I^2 = P*U^2
where P is Power in Watts, I is current in Amperes and U is voltage in Volts.
For example, to calculate a 100mA fuse-resistor I simply apply the formula above:
R = P/I^2 = 0.25W/(100mA)^2 = 25 Ohm / 1/4W, or
R = P/I^2 = 0.125W/(100mA)^2 = 12.5 Ohm / 1/8W, etc.
Of course, it is not that simple; but this is the principle of using fuse resistors.
-George