1. Legally enforceable. This means you have a legal obligation to carry something out that is set out in a contract. It is common to refer to a contract as a binding contract.
For example: When you sign the contract it becomes binding.
2. In skiing the binding is the thing that attaches the boot to the ski. More generally a binding is the thing maybe a string or cord that holds a number of other things together.
For example: A good pair of bindings is necessary if you are serious about skiing.
Cut the bindings and we'll see what is inside.
3. The spine of a book. A bookbinder binds books. There are some very beautiful tooled leather bindings.
For example: The bindings were made of pigskin decorated with gold leaf.
This book is falling to pieces it needs rebinding.
4. To bind is sometimes used in the sense of stop or force. It means that a person has obligations that stop them acting in a certain way. A person is bound by constraints.
For example: There is nothing binding you from emigrating. You have no family ties.