An ionic liquid is basically a liquid salt; in fact, they used to be called "molten salts." If you heat up table salt to 1,474 degrees Fahrenheit, for example, you'd get a type of ionic liquid. But they can also exist at much lower temperatures, and sometimes the term "ionic liquid" is restricted (somewhat arbitrarily) to chemicals that are liquid near room temperature. In any case, humans have created many, many different kinds of ionic liquids, which are used for all sorts of industrial processes, for example in batteries, electrolytes, sealants, and solvents.