Jerra is a popular misconception among many fans that that is the "last name" of Garet and all of his family members. It originated from one of Golden Sun's Debug Rooms, where a feature showing portraits of characters with their names attached shows Garet's four family members with the following names: Mr.Jerra, Mrs.Jerra, Kay Jerra, and Aaron Jerra. It has been found that this was the result of translation errors.
Garet's name in the Japanese version of Golden Sun games is comprised of katakana letters saying "Jerarudo", which transliterates as "Gerald", and that katakana is what he is identified as in the Japanese version's Debug Room. Garet's mother, however, says "Jera-mama", which is likely short for "Jerarudo-mama", which translates to "Gerald's Mother". It is the same story with "Jera-papa" ("Gerald's Father"), "Jera-otouto" ("Gerald's Brother"), and "Jera-ane" ("Gerald's Sister"). The family members names were likely rendered as shortened "Jera" names rather than full "Jerarudo" names because these were merely placeholder names for the Japanese developers of Golden Sun. In other words, Garet's family did not receive their own specific names in the Japanese release of Golden Sun.
When the game was translated for American release, however, Garet's family's contracted names were translated directly, with Jera suddenly becoming "Jerra", so that "Jera-mama" and "Jera-papa" became "Mrs.Jerra" and "Mr.Jerra", respectively. Following this, the translaters decided to give Garet's siblings their own first names of "Kay" and "Aaron", along with the Jerra corruption as their "last names". Because all these names would only be shown in the game's Debug Room, not normally accessible to players of the game, the names are not normally used in normal play.
"Jerra" was a point of controversy among the game's fanbase because it contradicts what seems to be a rule of nomenclature in the Golden Sun series: that all characters are identified by standalone names, with no "first name/last name" distinctions. While some believe it's nice to know that Garet and family seem to have a valid last name, opening up the possibilities for all the game's other characters to have last names, others feel very strongly that this counts as a translation error that goes against what the series otherwise presents as a uniform system of nomenclature.