A printer cartridge is a removable component used in inkjet and laser printers to supply ink or toner for printing documents and images. Inkjet cartridges contain liquid ink, while laser cartridges hold powdered toner. Each cartridge is designed to fit specific printer models and can vary in color and capacity. When a printer runs low on ink or toner, it may display a warning message, indicating that the cartridge needs to be replaced. Users can purchase new cartridges from various manufacturers or third-party suppliers, ensuring compatibility with their specific printer model for optimal performance.