Illuminator is an LCD backlight technology used in some Casio watches. The Timex corporation has its own similar technology called Indiglo. Casio originally used the Illuminator name for electroluminescent backlights, however it is now used for LED backlights also.
In response to the Indiglo backlight which Timex had introduced in 1992, Casio introduced in 1995 an electroluminescent backlight on its modules. One of the first models was the Casio DW-5600E, commonly known as the G-Shock Illuminator (where the "E" of the model number means Electroluminescent).
In reference to this, domestic models (Japan) would typically bear the term "Foxfire", while export models bore "Illuminator."