docs(angular): 📝 clarify eXtreme Programming definition

Author: yjaaidi

apps/cookbook/docs/angular/01-testing/02-designing-a-pragmatic-testing-strategy/index.mdx

@@ -224,7 +224,7 @@ Testing, and more precisely TDD, **keeps us focused on the task at hand, enablin
 
 ### The Wedding Registry Anecdote
 
-I had the privilege of being "born" into [eXtreme Programming](../../02-glossary.md#extreme-programming) _(XP)_. My first job _(back in 2007)_ was with a team deeply committed to XP values and practices. As the least experienced developer on the team, [Test-Driven Development](../../02-glossary.md#tdd) _(TDD)_ saved me _(among other practices)_.
+I had the privilege of being "born" into [eXtreme Programming](../../02-glossary.md#extreme-programming) _(XP)_. My first job _(back in 2007)_ was with a team deeply committed to XP values, principles, and practices. As the least experienced developer on the team, [Test-Driven Development](../../02-glossary.md#tdd) _(TDD)_ saved me _(among other practices)_.
 
 Thirteen years later, having always relied on testing and TDD, **I had to challenge my well-established assumptions**. What if we didn't need as much testing? Could there be situations where testing wasn't necessary at all? We don't need tests for a one-shot simple script or some [Spikes](../../02-glossary.md#spike), but we need tests for ambitious products, right? But where is the line?
 

apps/cookbook/docs/angular/02-glossary.md

@@ -29,7 +29,13 @@ Dogfooding is the practice of using your own product or service internally befor
 
 ## eXtreme Programming _(XP)_ {#extreme-programming}
 
-eXtreme Programming is a lightweight software development methodology that hasn't sold its soul to the devil of certification-driven business models.
+XP is a software development methodology that hasn't sold its soul to the devil of certification-driven business models.
+
+More seriously, XP is a lightweight software development methodology introduced by Kent Beck in the late 1990s. It is meant to improve software quality and responsiveness to changing requirements. Instead of trying to predict the future, XP embraces change, hence the subtitle of Kent Beck's book [eXtreme Programming Explained: Embrace Change](https://www.amazon.com/Extreme-Programming-Explained-Embrace-Change/dp/0321278658/).
+
+XP is based on the following set of values: Communication, Simplicity, Feedback, and Courage.
+These values are distilled into concrete principles like: Rapid Feedback, Assume Simplicity, Incremental Change, Embrace Change, and Quality Work.
+The whole translates into a dozen of practices that support each other like: Small Releases, Simple Design, Testing, Refactoring, and Collective Ownership.
 
 ## False Negative