A colloid is most often used to refer to either:
Colloidal: State of subdivision such that the molecules or polymolecular particles dispersed in a medium have at least one dimension between approximately 1 nm and 1 μm, or that in a system discontinuities are found at distances of that order. (IUPAC)
Colloid: Short synonym for colloidal system. (IUPAC)
A colloidal dispersion is a system in which particles of colloidal size of any nature (e.g. solid, liquid or gas) are dispersed in a continuous phase of a different composition (or state). The "name dispersed" phase for the particles should be used only if they have essentially the properties of a bulk phase of the same composition.
(http://goldbook.iupac.org/C01174.html)
Branch of Physics dealing with physical properties of colloidal systems (i.e. motion, forces, etc. at the scale of the colloidal system).
See book by Hunter - Foundations of colloid science