Magic (魔法 mahō) in the Nanoha universe refers to the shaping of magical energy (mana) into specific forms (spells) to achieve certain effects. As such, it is closer to science and technology than to mysticism.
Mana, the energy used to power magic, is generated within a mage's body, and its nature and capacity differs between people. One immediately visible difference, for example, is the "magic color", which determines the default tint of the released magical energy. While mana constantly generated within a mage's body is sufficient for most purposes, it can also be conserved in form of Cards or cartridges to be used later, especially for combat. Additionally, a small portion of released mana remains dispersed in the surroundings where it was used, and can be recycled for certain spells (e.g. Starlight Breaker).
People who undergo training and master magic are referred as "mages" or "knights". Before the magical energy can be used for a particular purpose, the mage shapes it into an appropriate form in a process known as "linking". For this purpose, all mages possess an organ known as Linker Core. Since efficient linking requires complex energy calculations, predefined magical "programs" known as "spells" are created to simplify the invocation of common magical effects. These programs are computed within the caster's brain, assisted by their Device (which can also serve as a storage medium for spells). The visual manifestation of these calculations is a magic circle, and when they are complete, a trigger is usually required to release the magical energy.
Once linked, the bonds of magic keep the energy together, unless dispelled or forcibly broken. An Anti Magilink Field (AMF) prevents the magical energy from being linked and such bonds, from forming. The EC Dividers have the shared function to break any magical bonds.
Apart from the regular magical linking, some mages display the Mana Conversion Affinity, i.e. the ability to spontaneously convert their generated mana into another form of energy (electricity, heat), bypassing the calculations that mages without MCA require to achieve the same effects.