Travel (or suitcase) organizers are square or rectangular fabric containers used to compartmentalize clothing while traveling. Not only do they save space, but most are designed to keep your clothes organized and wrinkle-free while they're packed.
They are usually made up of several buckets or bags of various styles and sizes, designed to store clothes, shoes, hygiene items or other essential items on your trips.
The best ones are made of really lightweight material so they don't add extra weight to your luggage, although there are thousands of different ones on the market.