An ion is an atom or molecule with a net electrical charge. The charge results from an imbalance between positively and negatively charged particles.
What this means at your property
The term appears in chemistry, smoke-alarm explanations and some air-treatment product descriptions. Those uses are not interchangeable. Knowing that equipment involves ions says little about the specific purpose, performance or restrictions of that equipment.
What should I ask about an ion-based product?
Request the actual model, intended application and manufacturer instructions. Compare a clearly defined function with the need at the property instead of treating a scientific term as proof of cleaning effectiveness.