The Peerage is the hierarchy of titles conferred by the English Monarch, dating back to Medieval times.
A peer of the realm is someone who holds one of the following titles (in descending order of rank): Duke, Marquess, Earl, Viscount, Baron.
These titles may be inherited, passed to the eldest son in a system known as male-preference primogeniture. Peerages of this type are hereditary peerages. Traditionally, hereditary peers were given automatic membership of the House of Lords, although this is no longer the case.
Peers whose titles cannot be passed on are known as life peers. They are not considered to be members of the nobility.
Another hereditary title which may be conferred by the Monarch is a baronetcy. Baronets use the title Sir; they are not ranked as peers.
The Peerage is also the abbreviated name of a reference book of British peers and baronets whose full title is Debrett's Peerage and Baronetage (sometimes known just as Debrett or Debrett's). This is the meaning of the term here. The Peerage may also be an abbreviation of books in the Burke's Peerage series, such as Burke's Peerage and Baronetage and Knightage which is also a reference book about British titled families.