Naming Day

Naming Day is one of the few known Matoran holidays. As the chief aspect of the celebration, specifically honored Matoran were recognized with a grant of a change in form to their names. The only known naming day was after the Bohrok crisis as a reward for the Matoran who did much during the crisis.

Name Changes
During the Naming Day after the Bohrok Crisis, four Matoran and a Ussal crab were given name changes in honor of their duties performed during the crisis. Jala was changed to Jaller, Maku was changed to Macku, Puku was changed to Pewku, and Huki was changed to Hewkii.

Maori controversy
The holiday was an in-universe way of expressing the name changes of certain BIONICLE characters, due to complaints by the Maori people (native islanders of New Zealand) who disapproved of LEGO's use of their words. As a result, a number of names were changed. LEGO came up with Naming Day Celebration as an in-universe explanation of the characters' name changes. LEGO also changed Tohunga to Matoran, giving the in-story reason that the Matoran had finally realized that they were one people, although the idea was later dropped and never remained canon.

Trivia

 * In "Fractures", the Coliseum is stated as the "home of Naming Day ceremonies", so it is believed some of these happened on Metru Nui.