What is the difference between tube and pipe?

Nominal Bore (NB) Pipe and stainless steel pipe fittings are measured in inches by the inside diameter of the hollow section of pipe, whereas tube and stainless steel tube fittings are measured by their outside diameter (OD).

Pipe is often used together with 150 psi Stainless Steel BSP Pipe Fittings, whereas tube is often used as handrail or for sanitary applications and made to AS1528 food grade standards.