TASK DEFINITION: In this task, we ask you to elaborate the sentence without changing its general meaning. You can do so by explaining further the input sentence, using more precise wording, adding qualifiers and auxiliary information etc.
PROBLEM: A federation is a union of a number of self-governing states or regions , which are joined together under a central government .

SOLUTION: A federation ( also known as a federal state ) is a political entity characterized by a union of partially self-governing provinces , states , or other regions under a central federal government ( federalism ) .

PROBLEM: A siddur is a Jewish prayer book .

SOLUTION: A siddur ( Hebrew : סדור -RSB- ; plural siddurim , -RSB- ) is a Jewish prayer book , containing a set order of daily prayers .

PROBLEM: Square rig refers to a type of sail and rigging where the sails are mounted on horizontal spars .

SOLUTION:
Square rig is a generic type of sail and rigging arrangement in which the primary driving sails are carried on horizontal spars which are perpendicular , or square , to the keel of the vessel and to the masts .