Short answers, pulled from the story.
A peerage is a legal system historically made up of hereditary titles, and sometimes non-hereditary ones, organized into noble ranks. It exists in numerous countries, including Australia, Belgium, Canada, China, France, Malta, Japan, Portugal, Spain, and the United Kingdom.
The United Kingdom's peerage splits into the Peerage of England, the Peerage of Great Britain, the Peerage of Ireland, the Peerage of Scotland, and the Peerage of the United Kingdom. Each covers titles created within a different time period, and in some cases a different kingdom.
A hereditary peer holds a title that can be inherited by an heir. A life peer holds a title within the peerage of the United Kingdom that cannot be inherited by anyone.
The Jacobite peerage refers to titles created following the deposition of King James II and VII from the thrones of England, Ireland, and Scotland.
A representative peer is a holder of a Scottish or Irish peerage who represented their wider peer group in the House of Lords at Westminster.
Scottish peers held a guaranteed seat in the House of Lords from 1964 to 1999, under the Peerage of Scotland.