When ever any class implements an interface or when ever a non abstract class extends a abstract class, the class should implement ( in other words define ) the methods in the interface or define the abstract methods in the superclass. ex:
If I may add my two cents, the word "to implement" also has another general meaning in programming. If you implement an algorithm or a method, it just means that you write the code for it.
Also, the dictionary you used is correct. The word "implement" can also be used as a noun to refer to any kind of tool. However, in this conversation, we are typically using the word as a verb instead.
An overridden method is one that has a different implementation than a method of the same signature in the parent class.
For example, the code below defines a method in a base class, then an extended class inherits from that base class and overrides the method to do something else.
The interesting (and useful) thing about this is polymorphism: The method is invoked based on the true runtime type of the object. For example, if an extended object is upcast to its base type, the extended method will still be invoked...
(For more information, search the forums for "polymorphism.")
"We're kind of on the level of crossword puzzle writers... And no one ever goes to them and gives them an award." ~Joe Strummer sscce.org