AC has different amounts of distortion depending on the method of production or transformance from direct current (DC). In general, modified sine waves indicate a cleaner current with less distortion than square waves.
Veteran electronics engineer, Lazar Rozenblat, explains that a power inverter converts DC power to AC. While square wave inverters are the least expensive, the low quality of the AC produced has largely excluded them from commercial use. Modified sine wave inverters produce an adequate quality current at an acceptable price. Modified sine wave inverters are actually modified square wave inverters.
While modified sine wave inverters are the most expensive of such devices, sensitive equipment such as laser printers, stereos and medical devices benefit from their quality. Square wave inverters are acceptable for hobbyists where such precision in the power source is not required.