A guardian ad litem, often referred to as a "GAL," is a person appointed by the court to represent the best interests of an individual. Unlike a guardian, a GAL does not manage the affairs of of persons, nor do they act as their attorney.
In a divorce or parenting petition proceedings, the GAL is usually appointed to represent the best interests of the children. The court charges the GAL with the responsibility of investigating designated issues and making recommendations to the court. Issues can include parenting responsibility, parenting schedules, ability of either parent, influence of significant others, and special needs of the children. The GAL is a valuable tool for the court since the GAL can gather a lot of information to provide to the court and aid in making a decision regarding parenting rights and responsibilities.
For more information on Guardian ad Litems, the New Hampshire guardian ad litem board has useful information on their site.