A nozzle (also called a tip) is an integral part of an injector. Depending on the application, it can be either a "Pintal" or a "multi-hole" design.
Early IDI (Indirect Injection) types of diesel and most gasoline engines are of the pintal design, which has an inverted conical tip on the end of the nozzle stem. This produces a conical spray pattern when the fuel is atomized. These injectors are mounted either in the intake manifold (multi-port) or in a "swirl chamber" in the head. However, they are not mounted with the nozzle directly in the combustion chamber.
The most common type of nozzle used in today's diesel engine is the multi-hole design. This nozzle is mounted directly in the combustion chamber, so they are in high pressure and temperature environment. If the injector is mounted concentrically in the center of the cylinder, then the holes are all located in a single plane or ring around the nozzle, equally spaced. If the injector is mounted at an angle, then the holes may be in two different planes, angled so the resulting spray pattern is concentric in the piston. Multi-hole nozzles may have a varying number and size of holes, depending on the combustion chamber, engine size, and horsepower requirements.