What is difference between Single user mode and Offline mode om SQL

1.When database is in offline users cant connect we need to bring our database in to emergency mode to connect to db for this we will try to bring in single user mode so that we can able to connect with single user.

2.Single user mode means access only SA admin,offline mode means no one user can not access.

3.To bring the database online from offline,there is no need of putting it in emergency mode.

4.If 
database in single user mode it will allow only one connection, it is in offline we can't do any thing.