An ink cartridge or inkjet cartridge is a replaceable component of an inkjet printer

Inkjet printer

An inkjet printer is a type of computer printer that creates a digital image by propelling droplets of ink onto paper. Inkjet printers are the most commonly used type of printer and range from small inexpensive consumer models to very large professional machines that can cost up to thousands of...

 that contains the ink

Ink

Ink is a liquid or paste that contains pigments and/or dyes and is used to color a surface to produce an image, text, or design. Ink is used for drawing and/or writing with a pen, brush, or quill...

 (and sometimes the print head itself) that is deposited onto paper during printing.

Each ink cartridge contains one or more partitioned ink reservoirs; certain manufacturers also add electronic contacts and a chip that communicates with the printer.
Most consumer inkjet printers, such as those made by Canon, HP

Hewlett-Packard

Hewlett-Packard Company or HP is an American multinational information technology corporation headquartered in Palo Alto, California, USA that provides products, technologies, softwares, solutions and services to consumers, small- and medium-sized businesses and large enterprises, including...

, and Lexmark

Lexmark

Lexmark International, Inc. is an American corporation which develops and manufactures printing and imaging products, including laser and inkjet printers, multifunction products, printing supplies, and services for business and individual consumers...

 (but not Epson) use a thermal inkjet; inside each partition of the ink reservoir is a heating element with a tiny metal plate or resistor.