"A set style of handwriting used in the royal chancery at Westminster for the engrossing of royal letters patent, writs and enrolments. Many government departments had their own set style of handwriting, which had evolved purely from a desire for distinctiveness, rather than concern for legibility. During the Commonwealth (1649-1660) such set hands were banned, along with the use of Latin in domestic administrative documents. Records were to be written in English and in an ordinary and legible hand. But the restoration of Charles II also restored all such set hands, which returned as idiosyncratic as ever. An Act of Parliament in 1731 (which came into force in 1733), declared that all records should be written in a common legible hand. The only exception was the enrolment of Acts of Parliament on Parliament rolls, for which Chancery hand continued to be used until 1836."
Quoted from http://www.nationalarchives.gov.uk/palaeography/doc10_popup/glossary.htm#Chancery