What type of capacitor allows for variable capacitance?

A variable capacitor is specifically designed to allow for adjustments in its capacitance value. This is achieved through mechanical means, such as moving plates or changing the distance between the plates, which alters the effective capacitance of the device. Such capacitors are commonly used in tuning applications, such as in radio frequency circuits where precise capacitance values are needed to select or tune into a desired frequency.

In contrast, a fixed capacitor has a predetermined capacitance value that cannot be changed. Switched capacitors, while capable of altering effective capacitance through switching configurations, do not provide the variable control that a variable capacitor does. Tuned capacitors pertain to components that help tune circuits to specific resonant frequencies, but they typically refer to a style of interaction with other components rather than a true variable capacitance feature on their own.

Thus, the fundamental ability of a variable capacitor to provide adjustable capacitance makes it the correct choice in this context.