Resonances are natural oscillations of bodies, spaces, oscillating circuits, etc. Natural oscillations are caused by physical properties, sizes, shapes and materials, by components and charge transformations.
All bodies have a more or less pronounced resonance, the frequencies of which can cover all frequency ranges: from infrasound to ultrasound to hypersonic, from Extremely Low Frequencies( ELF) over all frequency ranges to Dezi-millimeter waves.
Resonant frequencies can be generated, but they can also occur unintentionally and undesirably. For example, resonances of skyscrapers and bridges, body resonances and room resonances. What effects resonances have and what forces the natural oscillations release depends on how strongly the resonance is damped. For example, room resonances can strongly influence the sound image by overemphasizing certain frequencies, resulting in measures to absorb the resonances.
Technically, resonances are generated in oscillating circuits, resonators and oscillators. They also play an important role in antennas, filters, waveguides, in loudspeakers and speaker cabinets.