Jizyah is the Arab language translation of Poll tax - a tax per-person of other faiths. In the early days of the Ummayad Empire, this tax was applied to all non-Arabs, whether they had converted to Islam or not. This was amended by the successors of the Ummayads.
It was generally applied per male member of the non-Muslim community, and was often paid through their place of worship, where they were registered.
See also: dhimmi