means A device that converts digital data into signals that can travel over phone lines, cables, or other channels — and back again — so computers can talk across distances.

from A blend word, stitched from MOdulator and DEModulator: the two halves of what the device actually does, turning digital ones and zeros into wavering analog tones (modulation) and then unscrambling them at the other end (demodulation). It dates to the mid-20th century, born of early telephone-line data transmission, and the clipped name simply fuses the front of each function — a tidy bit of engineering shorthand.