What are the requirements for a child to travel with only one parent, specifically regarding the need for a notarized letter of consent from the absent parent?

When a child is traveling with only one parent, it is often required to have a notarized letter of consent from the absent parent. This letter should include details such as the dates of travel, destination, and contact information for both parents. It is important to check with the specific airline or country's regulations to ensure compliance with their requirements.