A line bundle is a vector bundle of rank (or dimension) , i.e. a vector bundle whose typical fiber is a -dimensional vector space (a line).
For complex vector bundles, line bundles are associated bundles of circle group-principal bundles.
The class of line bundles has a nicer behaviour (in some ways) than the class of vector bundles in general. In particular, the dual? of a line bundle is a weak inverse of under the tensor product of line bundles. Thus the isomorphism classes of line bundles form a group.