What is the difference between a Restricted Profile and a User in Android 4.3? Android 4.3 introduced a new feature called Restricted Profiles. What is a restricted profile, and how is it different from a User?
With 4.3, Android apparently has three types of user:


primary user (admin, owner)
secondary users
restricted profiles


Primary user is the first user created for the device, when setting it up.

All users (the primary user and secondary users) have pretty much equal control of the system - they can alter all the system settings, create more users, etc. but they cannot access the data or the apps* of the other users.

Since all users can only access their own data, they can also be linked to different accounts. Likewise, they could also use a same account if you set it up for each user individually. However, this doesn't make the device aware of the different users using the same account - each user has their own "link" to the account, unaware of the others.

A restricted profile is different. Like users, it has its own settings, and own data. However uses the primary user's accounts and installed apps. The primary user controls which of these are enabled for the profile.

Further, these profiles can be given parental-type restrictions to content - such as blocking all content defined as "mature". (Note: This requires support from the apps providing the content in order to work.)

* - Google Play app-store does sort-of support some inter-user data - when you install an app that another user already has, the same app code is used by both users. This means it doesn't need to be downloaded a second time, and doesn't take up extra space. It also means that when one of the users updates the app, it is updated for everyone. However, only thing shared between the users is the app code, the users cannot access each other's data.

More information on developer.android.com, see specifically: Support for Restricted Profiles.