Jargon buster!
ADD-ONS
Any one of a number of apps designed to enhance Kodi, such as YouTube support. Some add-ons are maintained by the Kodi developers. Others are created by the community.
SKIN
The visual interface for Kodi. You can change the default skin, Estuary, via the Addons browser.
KRYPTON
The codename for the current version of Kodi. The layout and menu options are different to previous releases.