To sever something or someone means to cut them off completely.
When we say "sever" we often talk about breaking ties or connections. For example, if two countries are at war, they might sever diplomatic relations with each other. This means that they're ending all communication and official contact between their governments. It's like cutting a rope - once it's cut, the connection is broken.
To cut free.
Example: After he graduated, he severed all links to his family.
