Question: In Groovy++ I often hear of the term Annotations. Can anyone explain me what is that in simple terms?

Answer: 
In short **It's a way to label a piece of code.** But it's not Groovy specific thing.

These labels can be used as meta-data by other applications to perform tasks like identifying unit test, dependency injection, or just a way to tell someone that a method is deprecated.

[Here](http://download.oracle.com/javase/tutorial/java/javaOO/annotations.html) is a link to some java documentation.
Some basic info to get you started.

<http://groovy.codehaus.org/Annotations+with+Groovy>