Views are specific to the tables for which they are created. When you create a table, four predefined views are created in addition by default: Personal Grid, Personal Split, Mobile, and Summary.
If you change one of your own personal views, it has no effect on other users' personal views. By contrast, if you change any other view you're allowed to edit, it affects all users with access to it. The two personal views start out the same, but one is set up as a split view, which opens the selected record in a preview pane.
Personal views aren't overwritten when default views are modified. If a team member using the team's default view makes changes, those changes are saved to the user's personal view. The user's personal view also isn't changed if updates are later made to the team default view, which enables users to have their own personal view and a team default view.
The mobile view shows only one field by default: Created By. The Mobile view cannot be deleted, but it can be edited. Mobile views are designed to be used when a user is viewing the system on a mobile device or when logged in with an ADA-compliant interface.
The summary view shows only two fields by default: Record ID and Creator Login. As with the mobile view, the summary view cannot be deleted, but it can be edited. The summary view is the default view until an admin applies a different default view for a team.