'permission by one hundred rabbis') is a term in Jewish law which means that one hundred Rabbis agree with a beth din (rabbinical court) that a particular situation warrants an exemption to permit a man to remarry even though his wife refuses or is unable to accept a get (a legal divorce according to Jewish law).
[1] In about 1000 CE the Ashkenazic halachic authority Rabbeinu Gershom of Mainz is said to have issued four decrees through his court.
"[2] Even though Rabbeinu Gershom, the leading authority of the age, decreed that a man was not allowed to divorce a woman against her will, the force of his decree was mitigated by later authorities who allowed for an exemption in certain extreme cases, in which they granted permission for a man to marry another woman if he received permission from 100 rabbis (meah rabbanim).
In the last century with the ease of communication, it has become a more formal process in which the beth din takes the lead and secures the one hundred signatures required.
[7] In 2019 the media reported that the Chief Rabbi of Israel delayed the funeral of Meir Kin's mother, until he agreed to divorce his first wife.