Permission defines the ability of an operation to have access on particular resources. They impose specific levels of authorization to a protected resource. The runtime security system defines permissions like File IO, Printing, Socket Access, Event Log, Web Access, User Interface and so forth.

What are Permission Sets?

Permission set is a collection of permissions which are used to modify the security policy for code groups. The CLR provides the following built-in permission sets.

Nothing        

Implies that the code cannot be executed.

Execution     

Implies that code does not have permission to access protected resources, but can execute.

Internet       

Implies that code downloaded from a location and has limited permissions.

LocalIntranet

Implies that the code holds permissions defined in the default enterprise policy.

Everything

Implies that the code has all permissions except to skip verification.

FullTrust

Code has full access to all system resources.