Materials science, also commonly known as materials science and engineering, is the Science and Engineering of material properties, their design, and uses.
A material, I think, most often refers to a type of Bulk matter (identified by its composition in terms of phases and chemical composition). However it may sometimes refer to chemical substances per se, or other non-bulk, but relatively simple, arrangements of matter, as for example, in Nanotechnology. It may even be used for more complex arrangements of matter so that a bulk description is not totally appropriate, such as in "smart materials", where ideas from Complex systems may be necessary for their description.
Materials science needs to describe the specific properties of each material. Constitutive equations play a fundamental role in the theory of these properties.
The physics of materials is based on Condensed matter physics. If dealing with fluids, it of course uses Fluid mechanics too.
Best materials course ever (mostly metals)
Virtual museum of minerals and molecules
See classification of materials in Condensed matter physics.
Some important materials: Polymers, Metals, Ceramics, Composite material.
See also Soft materials, Chemistry, Surface science
Some material properties:
See for a good resource on materials properties
Variational Methods for Microstructural Evolution
Some IUPAC definition recomendations: