Assignment of a variable (or its name) means giving that variable to a value as its name.
myField = ...
You can assign several variables to the same value and (if not final) you can assign the same variable to different values at different times. Read the assignment operator as "becomes equals to" or "receives the value of".
I think most people take initialisation to mean assigning a value to a variable or field in the same statement it is declared in.
Foo myField = new Foo();
subject: Difference between "Initialization" and "Assignment" ?