What is Master Of The Rolls?

Legal Definition
The Keeper or Master of the Rolls and Records of the Chancery of England, known as the Master of the Rolls, is the second most senior judge in England and Wales after the Lord Chief Justice, and serves as President of the Civil Division of the Court of Appeal and Head of Civil Justice. The position dates from at least 1286, although it is believed that the office probably existed earlier than that.

The Master of the Rolls was initially a clerk responsible for keeping the "Rolls", or records, of the Court of Chancery, and was known as the Keeper of the Rolls of Chancery. The Keeper was the most senior of the dozen Chancery clerks, and as such occasionally acted as keeper of the Great Seal of the Realm. The post evolved into a judicial one as the Court of Chancery did; the first reference to judicial duties dates from 1520. With the Judicature Act 1873, which merged the Court of Chancery with the other major courts, the Master of the Rolls joined the Chancery Division of the High Court and the Court of Appeal, but left the Chancery Division by the terms of the Judicature Act 1881. He retained his clerical functions as the nominal head of the Public Record Office until the Public Records Act 1958 transferred responsibility for it to the Lord Chancellor. One residual reminder of this role is the fact that the Master of the Rolls of the day continues to serve, ex officio, as President of the British Records Association. The Master of the Rolls was also previously responsible for registering solicitors, the officers of the Senior Courts.

One of the most prominent people to hold the position was Thomas Cromwell, a highly influential figure during the reign of Henry VIII. On 3 October 2016, Sir Terence Etherton succeeded Lord Dyson as Master of the Rolls.
-- Wikipedia
Legal Definition
Eng. law. An officer who bears this title, and who acts as an assistant to the lord chancellor, in the court of chancery.

2. This officer was formerly one of the clerks in chancery whose duty was principally confined to keeping the rolls; and when the clerks in chancery became masters, then this officer became distinguished as master of the rolls. Vide Master in Chancery.
-- Bouviers Law Dictionary
Legal Definition
In English law. An assistant judge of the court of chancery, who holds a separate court ranking next to that of the lord chancellor, and has the keeping of the rolls and grants which pass the great seal, and the records of the chancery. He was originally appointed only for the superintendence of the writs and records appertaining to the common-law department of the court, and is still properly the chief of the masters in chancery. 3 Steph. Comm. 417. Under the act constituting the supreme court of judicature, the master of the rolls becomes a judge of the high court of justice and ex officio a member of the court of appeal. The same act, however, provides for the abolition of this office, under certain conditions, when the next vacancy occurs. See 36 & 37 Viet. c. 66, ยงยง 5, 31, 32.
-- Black's Law Dictionary
Legal Definition
An assistant judge of the English chancery court, holding a court of his own next below that of the lord chancellor.
-- Ballentine's Law Dictionary