The term injection moulding process was coined at the start of the 19th century, coming from type foundry where this procedure was used in order to manufacture letters and word fragments. Uhlmann defined the process in his book "The Injection Moulding" (Berlin 1925) as the manufacturing process for moulded paddings that are manufactured as permanent moulds under pressure.

As the basic principle during the production of moulded paddings from plastic compounds is the same, this type of manufacturing was also adopted as "Injection Moulding Process". This definition portrays the essential features of the manufacturing process in a quite illustrative manner.

Forming can basically take place in two different ways: 1. through the purely mechanical, i.e. cutting and machining, processing 2. by applying pressure, whereby the compound is changed in between into a plastic state so that it adapts to the desired shape; i.e. through non-cutting forming.

The generally available plastic compounds can be divided into two main categories:
1. Temperable compounds that are liquefied by pressure and an increase in temperature far enough so that they adapt to the given mould; if, however, they remain at a certain temperature they become hard due to a chemical reaction and after having cooled down they finally keep the adopted shape. These compounds cannot be changed back into their plastic state and, by using pressure and heat, be formed once more. They are therefore defined as temperable or duroplastic plastics.
2. Non-temperable, so-called thermoplastic compounds, that, under pressure and an increase in temperature, become so soft that they fully adapt to a given hollow mould and when cooling down they change to the solid state by solidifying. These compounds underlie no chemical reaction whatsoever during the forming process and let themselves be formed as often as one likes by using pressure and heat (at least theoretically) once again. They are so-called reversible thermoplastic compounds.
As only these plastics are suitable for manufacturing in accordance with the injection moulding process, becoming malleable if heat is used on them, whilst not undergoing a chemical reaction towards induration, the manufacturing process is defined as the injection moulding process of thermoplastic compounds.