Nobility System of Harry Potter
Most Ancient and Noble
The Most Ancient and Noble Houses are the families that gained sovereignty from the muggle king Uther Pendragon of Camelot around 100 BC. Among these houses were the Houses of Pendragon, Olympian, Emyres, Gryffindor, Slytherin, Ravenclaw, and Hufflepuff. They took back the crown from King Uther, with his magical son King Arthur setting up the first magical community not under the rule of the muggle royal family, gaining this rank the nickname of the Founding Houses. These lines are almost extinct, with only the Houses of Hufflepuff, Gryffindor, and Slytherin having descendants so far disconnected that they probably don't know the connection. During their reign as the highest social rank, they were referred to as Dukes and Duchesses of the land.
Most Ancient
The Most Ancient Houses were families that already had roots in Magical Britania before the separation of the muggle and royal family lines but did not participate in the Camelot Wars or participate in the building of Magical Camelot. When Countess Ravenclaw decided that they needed a larger parliament to fairly decide the government of Magical Britain, they decided to reach out to the other local families. Among these families were the new Most Ancient Houses of Ollivander, Peverell, Ross, Blackwood, Dagworth, and Marchbanks. They were known as Marquis and Marquises.
Ancient and Noble
The Ancient and Noble Houses were houses added to the wizarding nobility after the Romans fully took control of the British Isles in 40 AD. To help represent the newer houses that came with the Romans. While some houses were able to keep their family names separate from the older houses like Clearwater, Greengrass, and Bones, some houses married into the old society, like the Potters and Longbottoms marrying into the House of Gryffindor, Gaunt marrying Slytherin, and Potter once again marrying into Peverell. This was also the first time a house was demoted. In 53 AD, there was a civil war within the Most Ancient House of Blackwood, separating them into two lines. The line that won renamed themselves as the House of Black, but was demoted to Ancient and Noble status because they had created a new house that would not meet the criteria for Most Ancient. These were known as Earls and Countesses.
Ancient
The Ancient Houses were houses added after the Roamsn left in 383 AD. It was stated that if a house could not rise in power while under the oppression of greater odds, as the muggle Roman Empire was hunting and drafting wizards into their army, then they should not be counted as noble as the ones who did. These houses included the Houses of Abbott, Goyle, Crabbe, Fortescue, Lovegood, and many more. They were considered as Barons and Baronesses.
Elder
Elder Houses were families that made a calling for themselves during the reign of King William the Conqueror who took over England. Magical Britain decided that they needed to adapt to the new culture that would surround them from the muggle side of their world. Among these houses were the Houses of Dumbledore, Weasley, LeStrange, Crouch, MacMillian, and others. The heads of these houses were considered Lords and Ladies. This is also the highest rank a lower-rank house can be promoted to. When one of the original Elder Houses(which unofficially but socially expected to call themselves the Elder and Noble Houses) becomes extinct, then a Minor House is voted on by the Elder and Ancient Houses to become an Elder House that cannot socially call themselves an Elder and Noble House. Few houses like the Houses of Selwyn, Fudge, and Prince have done this. This is also the lowest rank that is allowed to sit in the ruling parliament as nobility. During the reign of the Elder Houses, higher terms like Dukes and Barons were fazed out and even became taboo to introduce yourself with these titles in public.
Minor
Minor Houses are houses that joined Magical Britain after the death of King William the 1st. These houses included the Houses of Malfoy, Yaxley, Bulstrode, Nott, Scamander, Boot, and many others. They do not have any seats or positions within magical society and usually have to marry into an old house to have enough political sway with the houses that do have the notoriety. If a foreign magical family moves to Magical Britain, then they are allowed to call themselves the Lords and Ladies of a Foreign Minor House, like the Houses of Chang and Patil. The lower rank of Magical Houses can also be promoted to this level with enough time and work.
Magical
Magical houses are at the bottom of the social hierarchy. They are formed when a muggle-born has a child, making their former designation as someone from a family into the beginnings of a Magical House until they can build up enough history and accomplishments to be promoted to a Minor and possibly Elder House.