Niobium capacitors are types of electrolytic capacitors that are made from niobium oxide instead of traditional tantalum, offering a less expensive solution. They're used in nearly every area of electronics, are extremely stable and have a high resistance to overheating and breakdown.
The purpose of a niobium capacitor is to keep negative and positive charges separated from each other. If you take two electrical conductors and separate them with an insulator (a material that doesn't let electricity flow very well) then you have a capacitor: something that can store electrical energy. Its a bit like a battery, except a capacitor generally releases its energy much more rapidly – often in seconds or less.
You can choose from a range of shapes and sizes, but capacitors all usually have the same basic components. There are two conductors and the insulator in between them (called the dielectric). The two conductors inside a capacitor are wired to two electrical connections on the outside called terminals, which are like thin metal legs you can hook into your electronic circuit.