Mommy letter

A Mommy letter (or Mummy letter for European gatherings) is a letter sent (either on paper or electronically) shortly before a gathering (such as an Annual Gathering) giving information such as how to get to the gathering from the airport or train station, what unusual local laws might affect attendees' activities, and anything else that it is said that your mother would tell you if she were familiar with the details of the gathering and its host city.