A role is an attribute of a User (see also user for disambiguation) that signifies some right or responsibility the user has. A role shows up in three places in TiddlyWeb:

• As a list in the tiddlyweb.usersign hash.
  
• As a list on the User entity.
  
• As part of a policy.
  
  

A role is similar to a group, but the association is reversed. Whereas a group has a list of members (the users who are in the group), a user has one or more roles. In real world use the latter turns out to be a bit easier to manage (at least for the TiddlyWeb context). See I'm running a TiddlyWeb with lots of users and bags. How do I manage access control? for more information.