Specialised dictionaries are defined here by the specialised nature of the subjects they treat, focusing on particular subject fields, professional practices or even leisure activities such as sports with the aim of helping the user to acquire specialised knowledge, read specialised texts or engage in specialised translation. They can usefully be thought of as language for special purposes (LSP) dictionaries or special-purpose dictionaries, although the definition of LSP can be questioned as being too broad or subject to national variations. The theory of specialised dictionaries was elaborated first in the terminology tradition: Eugen Wuster in his posthumous handbook states that his aim is terminological lexicography. Specialised dictionaries can be monolingual, bilingual or multilingual. Monolingual dictionaries have no explicit translation function, though they can be used for translation. Wuster used the Universal Decimal Classification (UDC) for his machine-tool dictionary. In this case, the domain indication is represented by an index number.