What is the difference between share-level and user-level security?

Share-level and User-level security is actually in the category of computers.

In share-Level security systems, passwords are associated with specific objects, not with users.
ex. Windows XP

User-Level security is the most flexible and secure method of protecting the sensitive data, code, and design of objects in an Access database. User-Level security is for if you need more control.
ex. To prevent users from modifying the design of your tables and queries.