Does the voltage in the capacitor's description mean the ideal or maximum?

[Loomy]

I'm looking at a capacitor with the name "22R100 22uf 100V Electrolytic Radial Capacitor".

It has no description.

I would power it with 5V, is that alright or must I use 100V?

I'm wondering if 100V is the recommended or maximum voltage.

[MarkT]

Maximum working voltage.  You can use any voltage less than that so long as the polarity is right.

[DVDdoug]

And when you do have a maximum rating (voltage, current, or wattage) it's common practice to "de-rate" components.  That is, give yourself some safety margin.   If you have 16V, use a capacitor rated at 25V or more.   (25V is the next standard voltage.)

For resistors it's standard practice to use a resistor rated for at least twice the actual power dissipation.

[Klaus_K]

In a capacitor the capacity is a function of the area and distance of the electrodes. The closer the electrodes the higher the capacity, but the thinner the isolation. Capacitors with higher voltages require thicker or more expensive materials for the insulator, which makes them bigger and usualy more expensive.

For instance I have two 220uF capacitors like yours here from the same manufacturer.

25 Volt Variant 12 mm high and 8 mm diameter
35 Volt Variant 13 mm high and 10 mm diameter

So for 5V you could use a mechanically smaller capacitor than your 100V variant. If it is for slow power smoothing your 100V variant will be fine.

There are other factors like the speed at which you require the power. Thats why you will sometimes see capacitors with different values and materials put in paralell to each other.

[MarkT]

And when you do have a maximum rating (voltage, current, or wattage) it's common practice to "de-rate" components.  That is, give yourself some safety margin.   If you have 16V, use a capacitor rated at 25V or more.   (25V is the next standard voltage.)

For resistors it's standard practice to use a resistor rated for at least twice the actual power dissipation.

Most electrolytics are DC working voltage ratings, a 10V capacitor can be used indefinitely at 10V.  In other words you don't need to derate like you do with absolute maximum ratings of a semiconductor part.

Given the sparse range of voltages available you almost always have a safety margin through rounding up anyway.