From IFWiki

Quetzal stands for Quetzal Unifies Efficiently The Z-Machine Archive Language. Quetzal is also called the Z-machine Common Save-File Format Standard. It specifies how Z-machine interpreters should create a save-file. (Before the Quetzal standard, different interpreters used different save file formats, and couldn't load each other's.)

The Quetzal standard was created by Martin Frost.