Remanufactured ink cartridges are recycled cartridges that have been refilled by a 3rd party (not the original brand). This process is very environmentally-friendly, as every component of the original cartridge is either recycled with its raw materials extracted and used in the remanufacturing process, or reused and remanfucatured outright.
The remanufacturing process helps to keep plastics out of landfills, and conserves raw materials used in the production of ink cartridges such as timber, water, oil, petroleum, and various minerals.
See graphic below for a step-by-step explanation of the remanufacturing process.