Some manufacturers will refill printer cartridges and resell or return them to customers. Remanufactured cartridges, however, undergo a more involved process.
In the remanufacturing process, the cartridges are inspected and tested for function and quality before being refilled with fresh ink or toner. That being said, refilled cartridges can sometimes be lower quality than remanufactured cartridges. So, when purchasing cartridges, pay close attention to the terminology used in the description of the product.