From Aldersgate Street in London. On this street was a meeting place in which John Wesley had his heart-warming conversion experience on May 24, 1738. Charles Wesley only a few days before had also had a conversion experience in the same place. The building where the meetings took place no longer exists. Aldersgate Street has been shortened by common Methodist usage to simply Aldersgate. The word has come to represent both the place and the experience.
Source: A Dictionary for United Methodists, Alan K. Waltz, Copyright 1991, Abingdon Press. Used by permission.