'Henry VIII clauses' is a term used as parliamentary shorthand for any attempt by the Government to create for itself new powers to govern ‘by order’, thereby allowing future decisions to bypass proper parliamentary scrutiny.
Typically, it describes clauses in a Bill that would enable primary legislation to be amended or repealed by secondary legislation (e.g. statutory instrument) which may or may not be subject to parliamentary approval.
The expression is a reference to King Henry VIII's supposed preference for legislating directly by proclamation. The Statute of Proclamations 1539 gave Henry the power to legislate via Royal Proclamation rather than through Parliament.