Nozzle Vs Flanges

These two terms are somewhat related but are also different things.

Nozzle: For the process plant engineering and design this more commonly relates to an "Equipment Connection"
You will have suction and discharge "Nozzles" on pumps. You will have inlet and outlet "Nozzles" on exchangers. You will have many different "Nozzles" on vessels and tanks. the same goes for heaters, filters, compressors, etc. These "Nozzles may be "Screwed", "Flanged" or some other type of connection method.

Flanges: For the process plant piping and equipment engineering and design fields a "Flange" is a type of connection device. These "Flanges come in a specific range of "Classes" related to their strength based on the pressure and temperature. Flanges come in different configurations such as; Weld Neck, Slip On, Screwed (or Threaded), Lap Joint (or Van Stone). These are normally connected to pipe or pipe fittings. Flanges also come in two other configurations. These are the "Long Weld Neck which has a long neck and is often used by vessel manufacturers when making nozzles for vessels. The other is a one piece forging that includes the Flange (the connection point), the long Neck For the extension from the vessel shell to the flange) and a reinforcement shoulder (for the connection to the vessel shell).

You can see by this that there is a relationship between the two terms but you should also be able to see the difference.
Now why are you asking this question and what does it relate to?