The reluser table is used to track special relationships between accounts, such as community maintainers/moderators and their communities, which communities a user is allowed to post to, and which users are banned from commenting in specific journals. These relationships are defined as a single character in the database:
The reluser table is a non-clustered global table.
Its counterpart, the reluser2 table, is clustered.
Clustered relationship types are defined in
ljlib-local.pl, in the LJ::get_reluser_id function.
LJ::get_reluser_id description explains the numbering scheme;
no reluser2 types can be a single character.