JavaScript arrow and variables inside object

Here is the link to the exercise

https://www.codecademy.com/courses/introduction-to-javascript/lessons/advanced-objects/exercises/arrow-and-this

Can someone please simplify or explain this statement
“Arrow functions inherently bind , or tie, an already defined this value to the function itself that is NOT the calling object. In the code snippet above, the value of this is the global object , or an object that exists in the global scope, which doesn’t have a dietType property and therefore returns undefined .”