What is a printhead nozzle?
Nozzles, or "jets," are located on the printhead. There may be anywhere from 48 to 320 nozzles on any printhead, and each of them is smaller than a human hair.
Each nozzle is connected electronically to a heater (resistor) that heats and cools the ink inside the cartridge. When the ink is heated, a bubble is formed; when the heat is removed, the bubble bursts and sends ink dots through the nozzles and onto the paper in the printer.
This happens very quickly, creating dots that form print characters on the page at a rate of up to 6,000 drops per second. That is why you should never touch the nozzle or print head assembly with your fingers.