Dynamic Binding has several meanings in computing.
In the Lisp Language, it refers to a Variable Binding (association between a variable and its name) that has Dynamic Extent.
In many Object Oriented languages, it refers to a method call on an object being selected according to the dynamic type of the object – virtual functions in Cee Plus Plus, normal method calls in most other languages.
See also Simulated Dynamic Binding
See original on c2.com 
Dynamic Binding frees object-oriented programmers from having to manually encode Message Dispatch to different receiver types.