Permission, in the context of access, refers to the privilege to use some computer information. The use can be restricted to the viewing of information for some users, while, for other users, the ability to manipulate or alter the information may be granted.

Many operating systems, particularly those serving multiple users, have several different types of access privileges--a hierarchical scheme of permissions--that can be granted or denied to certain individual users or to groups of users.

Permission can be granted by means of a password. A password is a series of characters, selected by the user and known to them and a system administrator if one exists. If the user supplies the correct password, access is granted to the particular file, program or computer. Passwords are very useful in computer systems where there are many users, ensuring that unauthorized entry does not occur.