Automatically saves changes while editing a page, post or custom post type. Autosave was introduced in WordPress in version 3.6.
It also takes information from the user’s browser to confirm the changes to be saved automatically every 2 minutes.
Autosave is automatically enabled in your WordPress for pages and all post types. A new autosave for a post/page overwrites the previous autosave for that specific post/page in the database.
Also read: Complete WordPress Glossary