What is a patent specification?

A specification is the part of a patent application which describes the invention, identifying all parts and components of the invention, how they fit together, work, etc. For example, the specification for a patent covering a pencil would include a description of how the pieces of a pencil (wood, lead, eraser, etc.) fit together as well as a description of how a pencil is used (one end of the wood is sharpened to a fine point, exposing the lead contained within so that the lead can be used to place marks on paper, etc.).