What is Benefit Of Clergy?

Legal Definition
In English law, the benefit of clergy (Law Latin: privilegium clericale) was originally a provision by which clergymen could claim that they were outside the jurisdiction of the secular courts and be tried instead in an ecclesiastical court under canon law. Various reforms limited the scope of this legal arrangement to prevent its abuse. Eventually the benefit of clergy evolved into a legal fiction in which first-time offenders could receive lesser sentences for some crimes (the so-called "clergyable" ones). The legal mechanism was abolished in 1823 with the passage of the Judgement of Death Act which gave judges the discretion to pass lesser sentences on the first-time offenders.
-- Wikipedia
Legal Definition
English law. An exemption of the punishment of death which the laws impose on the commission of certain crimes, on the culprit demanding it. By modern statute's, benefit of clergy was rather a substitution of a more mild punishment for the punishment of death.

2. It was lately granted, not only to the clergy, as was formerly the case, but to all persons. The benefit of clergy seems never to have been extended to the crime of high treason, nor to have embraced misdemeanors inferior to felony. Vide 1 Chit. Cr. Law, 667 to 668 4 Bl. Com. ch. 28. But this privilege improperly given to the clergy, because they had more learning than others) is now abolished by stat. 7 Geo. IV. c. 28, s. 6.

3. By the Act of Congress of April 30, 1790, it is provided, §30, that the benefit of clergy shall not be used or allowed, upon conviction of any crime, for which, by any statute of the United States, the punishment is, or shall be declared to be, death.
-- Bouviers Law Dictionary
Legal Definition
In its original sense, the phrase denoted the exemption which was accorded to clergymen from the jurisdiction of the secular courts, or from arrest or attachment on criminal process issuing from those courts in certain particular cases. Afterwards, it meant a privilege of exemption from the punishment of death accorded to such persons as were clerks, or who could read.

This privilege of exemption from capital punishment was anciently allowed to clergymen only, but afterwards to all who were connected with the church, even to its most subordinate officers, and at a still later time to all persons who could read, (then called "clerks,") whether ecclesiastics or laymen. It does not appear to have been extended to cases of high treason, nor did it apply to mere misdemeanors. The privilege was claimed after the person's conviction, by a species of motion in arrest of judgment, technically called "praying his clergy."

As a means of testing his clerical character, he was given a psalm to read, (usually, or always, the fifty-first,) and, upon his reading it correctly, he was turned over to the ecclesiastical courts, to be tried by the bishop or a jury of twelve clerks. These heard him on oath, with his witnesses and comparators, who attested their belief in his innocence. This privilege operated greatly to mitigate the extreme rigor of the criminal laws, but was found to involve such gross abuses that parliament began to enact that certain crimes should be felonies "without benefit of clergy," and finally, by St. 7 Geo. IV. c. 28, § 6, it was altogether abolished.

The act of congress of April 30, 1790, § 30, provided that there should be no benefit of clergy for any capital crime against the United States, and, if this privilege formed a part of the common law of the several states before the Revolution. it no longer exists
-- Black's Law Dictionary
Legal Definition
Exemption from capital punishment to those connected with the church.
-- Ballentine's Law Dictionary