Official NATO Definition
The science of planning and carrying out the movement and maintenance of forces. In its most comprehensive sense, it is those aspects of military operations, which deal with:
the design, development, acquisition, storage, movement, distribution, maintenance, evacuation and disposal of materiel;
the movement, evacuation and hospitalization of personnel;
the acquisition or construction, maintenance, operation, and disposition of facilities; and
the acquisition or furnishing of services.
NATO Glossary of Terms and Definitions