Compact laundry generally refers to 24 inch washers and dryers. This size is convenient for stacking in closets or placing side by side in a standard 24 inch kitchen cabinet.
Almost all compact laundry is built and/or engineered in Europe. Europeans typically have smaller kitchens and living spaces, so compact laundry is a staple. Since these machines are only available in electric models, gas hook-up is not an option.