Okay, so a long time ago, there were people called bishops who were like special leaders in the Christian church. They were in charge of things like giving out sacraments and teaching people about Jesus. These bishops were important because they were chosen and ordained by other bishops who had been ordained before them, all the way back to the first bishops who were chosen by Jesus' disciples.
The idea of the historic episcopate means that we think it's really important for bishops to be ordained in this way, all the way back to those first bishops. Some Anglicans (which is a type of Christian denomination) believe that this is really important because it helps keep the church connected to its earliest roots and traditions. They believe that if the line of bishops was broken at any point in history, it could mean that the church isn't really following the original teachings of Jesus anymore.
So basically, the historic episcopate is the idea that the way bishops are chosen and ordained is really important, and that it should be kept going all the way back to the very beginning of the Christian church. Some Anglicans think this is super important to keep the church connected to its history and teachings.