What is the difference between a branch a denomination and a sect?

Denomination and sect are both Words which are used to describe smaller groups within a larger religious grouping. "Denomination" is used exclusively for sub-groups of Christianity, especially Protestant Christianity. "Sect" is used more for smaller and less mainstream groups, and for subgroups in non-Christian religions. "Branch" could also be used to describe a subgroup of a religion, but is perhaps more appropriate as a term for a group of subgroups. With respect to Christianity, for example, the Lutheran Church is a denomination, but is only one of a number of denominations which come under the umbrella term "Protestant". For this reason, "Protestant" might be described as a "branch" of Christianity.