Home wiki is a wiki project where an user is more active and is involved in a few local procedures. This definition leads us to think that a single user might have more than one home wiki if this user is active in more than one wiki. It is commonly where an user starts editing and have made more edits. However, a home wiki can also be automatically defined using some technical parameters like the number of edits and local flags. If an user doesn't have any local flags, it will be defined by the software according to the number of edits; if this user has sysop or bureaucrat's flag this parameter will get priority on the definition of home wiki. If the account on home-wiki is blocked, it is not possible to merge accounts and create a global account.
Global users 
It is important to define a home wiki of an user since it is related with a few global tools he or she might want to use. For example, if an user wants to be a steward, s/he has to demonstrate some knowledge on procedures that involves other projects than his/her home wiki. The community have to analyze the contributions and decide if s/he has enough experience outside his/her home wiki. Concerning that an user have to avoid using a global flag on a home wiki, this definition is important not only because of election procedures. Despite a controversial act have to be avoided on any wiki, an user should be even more careful when using this flag on his home wiki to avoid conflict of interests. Again, using steward flag as an example, they have to avoid changing rights on their home wikis and leave it to a more impartial steward.
- Contents of /trunk/extensions/CentralAuth/CentralAuthUser.php. svn.wikimedia.org