Bookmark object is a persistent version of a Share object. As a Share object is a ad-hoc reference to a current application state, Bookmark adds a name, title and description to a Share object. Thanks to it, Bookmarks can be listed on a Project page.
Bookmarks are listed before project's Views on Project page
Bookmark object is a wrapper of a Share. As you can see there are standard metadata fields and reference to a Share object:
Bookmark object syntax
"title": "My Store: Fort Shopping Center",
"description": "Bookmark to Fort Shopping Center store",
Bookmarks can be created by user in VIEWER, EDITOR or ADMIN role. Bookmarks are not shared among users, every user can list only his/her bookmarks.