A preset is a group of commonly-used settings that you use to quickly select the same settings in the future. Presets can store settings such as a postage class, an account and a graphic.
The maximum number of presets you can create is either ten or twenty one, depending on the software version your device uses. This includes the default preset.
For more information, see this page: Finding the software version
When your device enters sleep mode or when you switch it off it also keeps your last used settings.
UPDATED: 25 June 2021